Aslan Karatsev said finding stability off the court has helped him become the revelation of this year's Australian Open after the qualifier marched on to the semi-finals.

The Russian became the first qualifier to reach the last four of a major since Vladimir Voltchkov, famously in borrowed shorts, did so in 2000 at Wimbledon.

It was Pete Sampras who eventually blew away Voltchkov's threat at the All England Club on his way to another title.

And it turns out there is a connection between Karatsev and Voltchkov, with both men now calling Minsk their home.

But whereas Voltchkov is Minsk born and bred, Karatsev has taken a roundabout route to setting down roots in the capital of Belarus.

He explained on Tuesday how he was born in the Russian city of Vladikavkaz before moving as a toddler to Israel with his family and living there until the age of 12, when he and his father returned to Russia, spending time in the city of Taganrog.

Tennis took him to training bases in Moscow, then Halle in Germany, Barcelona, and finally Minsk.

It is in Minsk that Karatsev has linked up with former ATP professional Yahor Yatsyk, a man only one year his senior but already settling into coaching.

As Grigor Dimitrov succumbed to injury and slid to a four-set defeat against Karatsev on Tuesday, the unlikely figure in the final four reflected on his long road to this point.

"Yes, I was moving I would say too much," Karatsev said of his nomadic existence.

"In the end I found a coach, Yahor Yatsyk, and this is the right guy for me. He's helped me a lot, more the mental part, and then of course there is the technical stuff as well.

"I like to work with him. We're living in Minsk. We're practicing there."

Karatsev is the lowest-ranked man to reach a grand slam semi-final since Goran Ivanisevic, who won Wimbledon in 2001 on a wildcard entry while ranked 125th in the world.

His charge through the draw makes him only the second qualifier to advance to the Australian Open last four, after Bob Giltinan in December 1977.

"Of course it's amazing that I passed to the semi-finals from qualifying," Karatsev said. "I'm just trying to enjoy the moment and not thinking about that too much and playing from round to round."

He and Yatsyk set the goal of reaching the top 100, which Karatsev had not managed before getting to Melbourne.

Before this fortnight he stood at 114th in the rankings, but he will hurtle to a double-digit ranking next week.

"I think the key is to find the right team, the right coach that I found. I was really lucky to find him," Karatsev said.

"We just met in one tournament. We were saying, 'Okay, let's try to work together', and it's really a big luck that we started to work together and I have a good team around me."

Before he encountered Yatsyk, who as a player did not crack the top 1,000 in singles, Karatsev had a brief moment when he wondered if he might not make the grade.

"There was a time when I was injured that was a difficult time for me because I recovered after the injury, and then 2017 started, and I started to play again, and again I felt the knee," Karatsev said. "I said, 'Whoa.' I quit again for two and a half months, almost three, and I think this is the most difficult part."

Serena Williams is in the Australian Open semi-finals for the first time since she last won a grand slam title, beating Simona Halep to set up a mouthwatering clash with Naomi Osaka.

The American great gained revenge for her Wimbledon final defeat to the Romanian two seasons ago as she conjured a 6-3 6-3 win on Rod Laver Arena.

Halep dropped just four games in that stunning grass-court success in 2019, the third of four grand slam finals that Williams has lost since landing her 23rd major in Australia four years ago.

The 24th title has remained frustratingly elusive, with Williams one away from matching Margaret Court's record haul, but perhaps this is the week where that changes.

She must get past Osaka, her heir apparent as the figurehead for the women's game, but Williams showed her prowess in this match, devastatingly proving a point.

Her power won out, with 24 winners to just nine from Halep, although the 33 unforced errors from Williams showed there is room for improvement in precision.

The tone was set from the first point, Williams with a brilliant forehand service return winner on the forehand side on her way to an immediate break of serve.

Halep forced her way level but Williams raised the tempo in the sixth game and a deep forehand into the Romanian's backhand corner secured a 4-2 advantage.

Williams served out the set to love at the first opportunity but then dipped early in the second set, Halep pinching a break when the American volleyed waywardly at the net.

What proved a consistent theme was Halep's struggle to hit through her opponent, and the two-time grand slam winner could not capitalise on a 3-1 lead in that second set, dropping five successive games as the 39-year-old Williams began to turn on some vintage form.

Dismissive of the often weak Halep serve, Williams swept through to the clash with Osaka.

"I definitely think this was the best match I've played this tournament for sure," Williams said. "I had to, going up against the number two in the world. I knew I had to do better and that's what I did, so I'm excited."

Looking forward to facing Osaka, Williams said in her on-court interview: "She's such a strong player on the court and such an inspirational person off the court, which I think is really cool. I've been watching her and I'm sure she's been watching me."

Aslan Karatsev's Cinderella story and historic run continued after sensationally reaching the Australian Open semi-finals as Grigor Dimitrov struggled dramatically with injury on Tuesday.

Former world number three Dimitrov won the opening set and was on track to move through in Melbourne, but he faded alarmingly due to a lower back problem.

Karatsev capitalised to oust his much-more fancied opponent – who was barely able to walk afterwards – 2-6 6-4 6-1 6-2 on Rod Laver Arena, the Russian qualifier and world number 114 becoming the first man in the Open Era to reach the semi-finals on his grand slam debut.

The unheralded 27-year-old also became just the second qualifier to advance to the Australian Open last four after Bob Giltinan in December 1977 as defending champion Novak Djokovic or Alexander Zverev await.

Dimitrov was aiming to reach his second Australian Open semi-final and the final four of a slam for the fourth time in his career, and the Bulgarian star started well.

After being broken in the third game, 18th seed Dimitrov put the set back on serve immediately as he took control of proceedings.

Dimitrov fired down four aces, won 82 per cent of his first serves, hit six winners and made just five unforced errors, while Karatsev's unforced-error count hit 19.

But just as Dimitrov – who had not dropped a set en route to the quarters – looked like the man to beat, he wilted in remarkable scenes as Karatsev won the second set to level the match.

Dimitrov's first-serve winners dipped to 69 per cent – his second serve extremely problematic – while his unforced errors grew to 15 in the second set – and Karatsev took advantage.

The third set was a write-off for Dimitrov, who headed to the locker room for medical treatment after Karatsev cruised to a two-sets-to-love lead.

There were remarkable scenes in the third set, Dimitrov virtually conceding as he was unable to keep up with Karatsev due to the injury.

Dimitrov, who only won 12 points in the third set as he was unable to keep up with Karatsev or generate any power on his serve, emerged for the fourth set but, while he tried to will himself on, it only delayed the inevitable in sad scenes.

Data Slam: Karatsev joins Russian club
Karatsev became the fourth Russian man to reach the Australian Open semis in the Open Era, after Aleksandar Metreveli  (1972),  Yevgeny  Kafelnikov  (1999-2000)  and  Marat  Safin  (2002, 2004-05). He is also the lowest-ranked man to reach the semi-finals of a major since Goran Ivanisevic (125) at Wimbledon in 2001.

WINNERS/UNFORCED ERRORS
Dimitrov – 21/34
Karatsev – 34/44

ACES/DOUBLE FAULTS
Dimitrov – 9/7
Karatsev – 9/6

BREAK POINTS WON
Dimitrov – 4/14
Karatsev – 8/11 

Former world number one Naomi Osaka is unfazed about her record at grand slams as she eyes consistency after reaching the Australian Open semi-finals.

Osaka will face either 23-time slam champion Serena Williams or Simona Halep in the semis following Tuesday's emphatic 6-2 6-2 win over Hsieh Su-wei in Melbourne.

Three-time major winner Osaka has gone on to win the title each time she has reached the quarter-finals of a slam – beating Hsieh en route to her 2019 Australian Open triumph.

Asked about the record, Osaka told reporters: "I don't really care about the stat. Just because I've only been to four quarter-finals.

"It feels something like 20. That would be cool. But four, it's not really doing too much for me.

"I would be more impressed if I didn't lose in finals. If it says 10-0 in finals. But the fact is if I don't reach the finals, I lose in the fourth round or the third round.

"For me, I'm happy to be more consistent. I think I'm being more consistent since New York, so that's the ultimate goal for me."

Osaka – in the midst of a 19-match winning streak – overpowered veteran Hsieh on Rod Laver Arena, where the Japanese star hit 24 winners and just 14 unforced errors, while she lost just two of her 25 first-service points.

It does not get any easier for Osaka, with record-chasing Williams or two-time slam champion Halep standing in the way of a trip to Saturday's decider at Melbourne Park.

"I played both of them before I think multiple times," Osaka – confident after saving two match points against Garbine Muguruza in the last 16 – said.

"Halep, I don't really like playing her. She's someone that's really tough, someone that gets the ball back every time. For me it's definitely a mental and physical battle.

"Of course, the same goes for Serena. She's Serena, someone that I feel really intimidated when I see her on the other side of the court."

Former world number one and two-time grand slam champion Yevgeny Kafelnikov believes it is "inevitable" that a Russian player will claim major success as the country's male trio flourish at the Australian Open.

For the first time in the Open Era, three Russian men advanced to the quarter-finals of a slam thanks to star Daniil Medvedev, Andrey Rublev and qualifier Aslan Karatsev in Melbourne.

World number four Medvedev – the 2019 US Open runner-up – will face countryman Rublev in the Melbourne Park quarters as Karatsev meets Grigor Dimitrov for a spot in the semi-finals.

Not since Marat Safin at the 2005 Australian Open has a Russian male won a slam, but Kafelnikov is excited about the future.

"We all know that it's inevitable that they're going to win a slam," Kafelnikov, who was the first Russian man to earn a grand slam singles championship via the 1996 French Open before reigning supreme at Wimbledon three years later, told ATPTour.com.

"It's a question of when and where."

Kafelnikov added: "It was really expected that two of them got to where they are. The third one is a big surprise, but a very happy surprise. I'm very happy for Aslan, finally getting his breakthrough.

"He's going to play a lot of tournaments now without any pressure for the remainder of the 2021 season in terms of getting into the main draws and a big pay cheque will also be a huge boost for him. I'm really happy for him."

Kafelnikov, who won 26 singles titles, continued: "To be honest, I would be happy if one of those guys or even both of them surpass me in terms of number of titles and weeks at number one in the world.

"I'd be happy. I'm not going to be jealous about it. My career was very successful, and hopefully they will have even better [careers]."

Former world number one Naomi Osaka was relentless as she dismantled Hsieh Su-wei to reach the Australian Open semi-finals 6-2 6-2.

Hsieh upstaged the likes of 2019 US Open champion Bianca Andreescu en route to the quarter-finals, but the veteran was overpowered by Japanese star Osaka in Melbourne on Tuesday.

Three-time grand slam champion Osaka dominated from the outset, especially on serve – losing just two points on her first serve, as the third seed awaits record-chasing Serena Williams or Simona Halep in the final four at Melbourne Park.

Osaka emerged from the jaws of defeat in the last 16, saving a pair of match points to claim an improbable victory against last year's runner-up Garbine Muguruza.

And Osaka was a woman on a mission in sunny and warm conditions on Rod Laver Arena, where the 23-year-old broke for an early 3-1 lead.

Hsieh – the oldest player in the Open Era to make her grand slam quarter-final debut, aged 35 – had the chance to break back immediately, but Osaka held firm after fending off a pair to consolidate.

Osaka, who has gone on to win the title each time she has reached the quarter-finals of a major – beating Hsieh en route to the 2019 Australian Open crown, had another two break points saved but she still cruised in the first set.

It was a powerful but disciplined performance from Osaka, particularly on serve as she won 100 per cent of her points on first serve (12 of 12) against a helpless Hsieh.

The second set followed a similar theme – Osaka maintaining her dominance as she raced out to a 3-0 lead.

Osaka never relinquished the break, closing out the match on Hsieh's serve, with the six-time WTA Tour champion improving to 4-0 in quarter-final matches at slams, and 2-0 at the Australian Open.

Data Slam: ​Osaka extends streak
Eyeing a second Australian Open trophy, Osaka has now won 19 consecutive matches, dating back to February last year following the Tour's resumption amid the coronavirus pandemic. She last lost while on Fed Cup duty with Japan.

WINNERS/UNFORCED ERRORS
Osaka – 24/14
Hsieh – 14/23

ACES/DOUBLE FAULTS
Osaka – 7/1
Hsieh – 0/3

BREAK POINTS WON
Osaka – 4/12
Hsieh – 0/3

A third consecutive Australian Open quarter-final beckons for Ash Barty but the world number one is far from satisfied as she eyes a drought-ending title in Melbourne.

Barty produced a masterclass to blitz American Shelby Rogers 6-3 6-4 in the fourth round on Monday.

Not since Wendy Turnbull in 1984 has an Australian woman reached three successive quarter-finals or more at Melbourne Park, where Barty will meet Karolina Muchova in the last eight.

But 2019 French Open champion Barty is dreaming big as she looks to become the first Australian woman since 1978 to take the title.

"We're not done yet," Barty,a semi-finalist last year, said. "Obviously it's exciting to be in another quarter-final of a grand slam, particularly here in Australia.

"If we had looked at the way we were preparing during our pre-season, to have the start that we have had so far is really encouraging, but certainly not satisfied with where we're at at the moment. 

"We will keep chipping away and keep trying to do the right things to progress as far as we can."

Barty arrived in Melbourne at the start of the year having not played in a competitive WTA Tour event since February 2020 due to the coronavirus pandemic.

Asked about the prolonged break, Barty – who stepped away from tennis in 2014 before returning in 2016 after playing cricket – said: "I think I know that I've done the work. I know that we prepared in the right way during the pre-season. 

"We've done all the work to try to give myself the opportunity to play a good level of tennis and to a level that I know I'm capable of. It's just knowing that I put the trust in the work that we've done, more than surprising myself.

"I think I've known that I've done the work. I have the ability to play at this level and then it's just about going about all of our processes, our routines the right way. All of those came back quite naturally.

"It's something that I've practiced a lot, and I gain my confidence from that practice and from those preseasons as opposed to just match results."

Jessica Pegula said she "can't be more confident" after upsetting Elina Svitolina to reach her first grand slam quarter-final and Ash Barty stayed in the hunt for Australian Open glory on Monday.

Pegula, the daughter of NFL and NHL franchise owners of the Buffalo Bills and the Sabres, beat fifth seed Svitolina 6-3 3-6 6-3 on Rod Laver Arena to set up a showdown with her fellow American and friend Jennifer Brady.

Brady made it all the way to the semi-finals of the US Open last year and has now put together her best run at Melbourne Park after seeing off Donna Vekic 6-1 7-5.

World number one Barty has not dropped a set in her home major and started the second week by dispatching Shelby Rogers 6-3 6-4.

The top seed from Queensland's next assignment will be a meeting with Karolina Muchova, who saw the back of Elise Mertens 7-6 (7-5) 7-5.

Muchova, the 25th seed from the Czech Republic, has made it through to her second grand slam quarter-final - having also reached this stage at Wimbledon in 2019 - without losing a set.

Pegula to put friendship to one side

Pegula and Brady are close friends, but they will have to put that to one side when they meet in the quarter-finals.

The world number 61 claimed her first victory over an opponent ranked in the top 10 just over a month after Svitolina beat her in straight sets in Abu Dhabi.

Pegula hit 31 winners to Svitolina's 19 and won 21 points from 29 when she made a trip to the net as she broke new ground at a major

She said: "I can't get more confident, it's my best result yet and I'm playing good tennis. Today was a hard-fought win, so, yeah, feeling pretty good."

Pegula added on the prospect of facing Brady: "We're here to have fun and compete. If I can do it against somebody that I like, that I wouldn't mind if they beat me, hopefully not, but if they did, why not?"

Brady benefited from strict lockdown

Many players understandably struggled during and after being in a strict two-week lockdown in a hotel room following their arrival in Australia.

Brady was among the players who were not allowed out of their rooms for a fortnight, but said she used the situation to recharge her batteries before the first major of the year.

The 22nd-seeded Pennsylvanian said: "I think it was a little bit of a benefit for me, just taking a break from tennis. I had been going non-stop since World Team Tennis in June. I didn't take any time off.

"I was playing from June and then played US Open, the U.S. tournaments, and then went straight to Europe, then finished there and was training in Europe, then went home for Christmas and then came and started in Abu Dhabi.

"So obviously I didn't really feel super fresh mentally coming into Abu Dhabi. And then when I was away from tennis for two weeks, I felt like I wanted to play again to compete and I think that helped me."

Much improved Czech

Muchova had not been beyond the second round of the Australian Open before last week but now has a semi-final spot in her sights.

The 24-year-old was 4-0 down in the opening set as Mertens got off to a flyer but warmed to the task with her battling spirit and positive approach.

Muchova converted five of the six break points she earned on Margaret Court Arena, also coming from a mini-break down in a first-set tie-break.

She struck 25 winners to Mertens' 15 and advanced despite making 31 unforced errors, getting her rewards for throwing caution to the wind.

World number one Ash Barty secured another quarter-final berth at the Australian Open after outclassing Shelby Rogers 6-3 6-4.

It was a Barty party on Rod Laver Arena, where the 2019 French Open champion dominated from the outset to see off unseeded American Rogers in a little over an hour on Monday.

Barty, who appeared in the semi-finals in Melbourne last year to become the first Australian woman to reach that stage since Wendy Turnbull in 1984, raced past Rogers to set up a meeting with Karolina Muchova.

Home hope Barty and Rogers renewed acquaintances behind closed doors in the last 16 after the former won a match tie-break against last year's US Open quarter-finalist en route to claiming the Yarra Valley Classic.

Barty was unstoppable from the start, striking first in the fourth game and breaking for a 3-1 lead after precision play left Rogers helplessly scrambling around the court.

There was a test for Barty after Rogers earned a pair of break points in the seventh game, but the former saved both.

It was the only real challenge in a first set controlled by Barty, who continued where she left off in the second.

While Rogers showed glimpses, Barty – moving freely with all eyes on her heavily strapped thigh – was firmly in the groove as she broke for a 2-1 lead.

Another break followed but there was a blip for Barty, who was broken for the first time when serving for the match at 5-2 in a late Rogers resistance which only delayed the inevitable.

Data Slam: ​Three in a row for Barty
Barty will contest her third consecutive Australian Open quarter-final. Not since Wendy Turnbull in 1984 has an Australian woman enjoyed such a run. Barty is bidding to become the first Australian woman to win the grand slam since 1978.

WINNERS/UNFORCED ERRORS
Barty – 21/16
Rogers – 14/25

ACES/DOUBLE FAULTS
Barty – 5/3
Rogers – 5/1

BREAK POINTS WON
Barty – 3/6
Rogers – 1/3

Rafael Nadal insisted he is not "obsessed" in his quest for further grand slam glory after the 20-time major champion moved through to the Australian Open quarter-finals. 

Nadal advanced to the last eight of the tournament for the 13th time in his illustrious career following Monday's dominant 6-3 6-4 6-2 victory over 16th seed Fabio Fognini.

World number two Nadal is bidding to claim a record 21st slam crown, while the Spanish star is also looking to become the first man in the Open Era to win each of the four majors twice.

As Nadal looks ahead to a showdown with fifth seed Stefanos Tsitsipas, he discussed his motivations, having won everything on offer on the ATP Tour.

"I play tennis. I like tennis," the 34-year-old said. "I like what I am doing. That's the main thing. 

"Of course I am very motivated to win grand slams and to play in the most important events of the year. No doubt about that.

"The only thing that I said is I have never been obsessed to try to be the best or to try to – no, I just did my way. That worked for me.

"I think the ambition is important, to have an ambition, but a healthy ambition. If you have too much ambition then you can be frustrated when you are not able to achieve all the things that you wanted.

"I never approached the sport and my career that way. That's it. I enjoy, I give my best always. I try to compete at my highest standards every day. Sometimes the highest standards are 60 per cent, sometimes they are 100 per cent. But I just try to give my best throughout my career, and that's it.

"For me the main thing is come back home with personal satisfaction that you gave it everything. That's what gives me happiness and makes me stay calm."

Nadal was under an injury cloud heading into the year's first grand slam due to a back problem which forced him to sit out Spain's ATP Cup campaign in Melbourne.

But the 2009 Australian Open champion has looked comfortable at Melbourne Park, where he is yet to drop a set.

"I played first set without a doubt [against Fognini] has been my best level in the tournament," Nadal said. "It's normal, too, because I was able to practice for two days in a row. That makes an important difference. 

"But at the same time, it's important to find positive feelings now. My physical condition needs to keep improving. But I think this match helps, too.

"I was not able to practice the proper way for the last 19 days, but yesterday [Sunday] I started again to increase the amount of work on the practice, and today has been a positive victory with some long points, so that helps for the next match."

Rafael Nadal's bid to win a record 21st grand slam title remains on track, while there is a distinctly Russian flavour to the quarter-final line-up at the Australian Open.

World number two Nadal eased past Italian 16th seed Fabio Fognini behind closed doors at Melbourne Park in sunny and warm conditions on Monday.

Daniil Medvedev and Andrey Rublev ensured Russia made history en route to the quarters in Melbourne.

FAMILIAR TERRITORY FOR NADAL

Nadal reached the Australian Open quarter-finals for the 13th time in his career after outclassing Fognini 6-3 6-4 6-2 on Rod Laver Arena.

Stuck on 20 slam championships alongside Roger Federer, who is absent in Melbourne, Nadal is also looking to become the first man in the Open Era to win each of the four majors twice.

The 2009 Australian Open champion was too good for Fognini as Nadal continued his fine run of not dropping a set en route to the last eight in 2021.

Only at the French Open, where he is a 13-time champion, has Nadal reached the quarter-finals more often (14) than at the Australian Open. Federer (15) and John Newcombe (14) are the only men to have reached more Australian Open quarter-finals.

Nadal, who hit 24 winners against Fognini, will face fifth seed Stefanos Tsitsipas for a place in the semi-final after ninth seed Matteo Berrettini withdrew with an abdominal strain before Monday's showdown.

HISTORY FOR RUSSIA​

For the first time in the Open Era, three Russian men have advanced to the quarter-finals of a slam.

Medvedev – the fourth seed – and Rublev joined countryman Aslan Karatsev in the last eight following their respective triumphs on Monday.

Runner-up at the 2019 US Open, Medvedev made light work of American Mackenzie McDonald 6-4 6-2 6-3, extending his winning streak to 18 matches as he reached his maiden Australian Open quarter-final.

"It's an exciting moment to be in the quarters in Australia for the first time. That's a great achievement for me," Medvedev said.

"I want more all the time, but step by step. So this is amazing … I finished at 1.30 [hours], which is important in the later stages of the grand slams, to make fast matches."

It will be an all-Russian affair in the quarters after seventh seed Rublev benefited from a walkover.

Rublev was leading 6-2 7-6 (7-3) when Norway's Casper Ruud retired on Margaret Court Arena.

"At least one of us will be in the semi-finals. So it's good news but yeah, it's going to be a tough match," said Rublev, who featured in last year's French Open quarter-finals.

"Last time he beat me in the quarters in the US Open. So now we're in the quarters in the Australian Open, so we'll see what's going to happen."

Rafael Nadal reached the Australian Open quarter-finals for the 13th time in his career with a straight-sets win over Fabio Fognini.

The Spanish star again looked in strong form in a 6-3 6-4 6-2 victory over Italian 16th seed Fognini behind closed doors on Rod Laver Arena on Monday.

Nadal, who is aiming to win a men's record 21st grand slam title in Melbourne, is yet to drop a set at the year's first major and beat Fognini for the 13th time in 17 meetings.

The world number two will face either Stefanos Tsitsipas or Matteo Berrettini in the last eight.

Nadal gave up an early break lead against Fognini but a powerful forehand return led to another and a 4-2 lead.

Despite serving at just 42 per cent, Nadal closed out the opening set.

Fognini was unable to consolidate a break lead in the second set, having led 4-2, before Nadal recovered from 0-40 down to hold in the eighth game.

That would prove a decisive hold, Fognini blasting a ball into the stands after netting a volley to give Nadal a break point, converted when a forehand went wide before the Spaniard secured the set.

Fognini handed Nadal his only loss from two-sets-to-love up at a grand slam at the US Open in 2015, but a break for 2-1 in the third saw the latter end any chances of a repeat on his way to a convincing win.

Data Slam: Nadal's fine Australian Open record
Only at the French Open, where he is a 13-time champion, has Nadal reached the quarter-finals more often (14) than at the Australian Open. Roger Federer (15) and John Newcombe (14) are the only men to have reached more Australian Open quarter-finals.

WINNERS/UNFORCED ERRORS
Nadal – 24/20
Fognini – 32/35

ACES/DOUBLE FAULTS
Nadal – 6/3
Fognini – 7/3

BREAK POINTS WON
Nadal – 6/19
Fognini – 2/6

Serena Williams is moving better than she has in years, according to her coach Patrick Mouratoglou.

Williams, 39, has looked in good form at the Australian Open as she eyes a record-equalling 24th grand slam singles title.

The American has dropped just one set on her way to the quarter-finals, in which she faces Simona Halep on Tuesday.

Mouratoglou said Williams' movement was the best it has been in several years.

"First of all, it's something that we have put the emphasis on because in tennis that's probably one of the most important things. If you are late on the ball, you can't do what you want to do. Sometimes you don't even touch the ball," he told a news conference on Monday.

"It's a sport where you have to be able to move fast from side to side and long enough. It's something that probably in the last two, three years, this had consequences for Serena.

"Even more, when you're not in a good day, you need a plan B. To be able to have a plan B, you have to be able to move well. If you can't move well, there is no plan B. The only plan is attack.

"I think it cost her a few important matches. So we have decided to find a way to bring back the footwork that she used to have in the past. I feel like she's done a great job. She's moving much better."

Williams last won a major title in Melbourne in 2017, losing four grand slam finals since then.

With all eyes on her as she aims to equal Margaret Court's record of 24 grand slam singles titles, Mouratoglou insisted that mark was not an obsession for Williams.

"Does she need that validation? I don't think she needs that validation.  But, I mean, clearly she came back to tennis to win some other grand slams, so that's for sure the goal," he said.

"Now, she's not as obsessed with the 24 than most of the people in the tennis world, but definitely she wants to win grand slams. That's the only reason why she came back to tennis."

Novak Djokovic fought into the quarter-finals of the Australian Open despite concerns over a muscle injury, seeing off Milos Raonic in four sets.

Djokovic's hopes of defending his title appeared to be in doubt when he said he had a "muscle tear" and was unsure whether he would play the fourth-round clash.

But his history of dominance over Raonic was perhaps a motivating factor in him taking to the court and he stretched his head to head lead to 12-0 with his 300th grand slam win, becoming only the second player in history to reach the landmark.

He did not have it all his own way, a spirited Raonic levelling matters in the second set after losing the first on a tie-break.

However, Djokovic was in control thereafter, progressing 7-6 (7-4) 4-6 6-1 6-4, though a last-eight meeting with Alexander Zverev may prove a sterner test.

Djokovic made it eight wins in nine in tie-breaks with Raonic to take the first set and things looked bleak for the Canadian when he received treatment on his foot in the second set.

But that break proved just the tonic for Raonic as he went on to win a set against Djokovic for the first time in four grand slam meetings.

Yet the tide turned emphatically back in Djokovic's favour in the third – the Serbian winning five straight games to move into a 2-1 lead.

His success came through a familiar strategy against a player of Raonic's power on serve.

Djokovic wasted few opportunities to punish the second serve and consistently took Raonic out of his comfort zone by forcing him into long rallies.

Raonic, to his credit, did save four break points in the fourth set but the dam finally burst and he could not prevent Djokovic from snatching the fifth chance that came his way, the world number one ensuring there was to be no shock as he reached another milestone in a remarkable career.

Data Slam: Djokovic's delightful dozen

Djokovic is through to a 12th quarter-final in Melbourne, the eight-time winner last failing to reach the stage in 2018, when he lost to Hyeon Chung.

WINNERS/UNFORCED ERRORS
Djokovic – 41/25
Raonic – 50/35

ACES/DOUBLE FAULTS
Djokovic – 10/3
Raonic – 26/3

BREAK POINTS WON
Djokovic – 3/11
Raonic – 1/3

Simona Halep set up a quarter-final duel with Serena Williams after showing admirable character to battle back from a set down to beat Iga Swiatek 3-6 6-1 6-4 and seal her 100th grand slam match win.

Halep and Swiatek put on a thrilling show in the night session on Sunday, as the Romanian two-time grand slam champion demonstrated her fighting spirit to come from a set down and reach the last eight.

Swiatek took charge in the first set after saving the first two break points of the contest, eventually putting herself in a commanding position as she won the 10 of the final 11 points of the set, but Halep remained focused as her 19-year-old opponent began to wobble in the second.

Halep then snuffed out any threat of a turnaround by breaking back straight after losing on her own service in the decider and she went on to set up a meeting with Williams, who had overpowered Aryna Sabalenka earlier in the day.

Naomi Osaka also advanced, though she was by no means comfortable, while Hsieh Su-wei beat Marketa Vondrousova in straight sets.

HALEP'S REVENGE

Halep's clash with Swiatek was their first since the French Open last October, when Swiatek ran out a 6-1 6-2 winner and went on to claim her maiden major title.

Revenge was on the cards at Melbourne Park and Halep got the job done impressively, showing her mettle to return from a set down.

"Well, I thought before the match that I have to be a little bit more aggressive than Paris. In Paris I have been very far back, and my ball didn't go through the court," the second seed said. "So, I thought that it's a better chance to go and hit.

"The pressure came from the way I played the last match against her. I just expected a better game from myself, which I did, and I'm really happy about that."

Halep accepts facing Williams will be an entirely different challenge, but she remains confident despite lauding the American a "legend" in her on-court interview.

"Of course it's different, she's the only one with 23 grand slams, so you cannot compare Serena with all of us, because we do not have so many grand slams," Halep added.

"But when I step on the court, it's just another opponent, and always I'm focused on myself more than I focus on who I play. We played so many times. I know what to expect. I will just try to do my game, and I will be confident."

WILLIAMS ON COURSE

All eyes are on Williams yet again, as she hopes to equal Margaret Court's record of 24 grand slam titles – and on the evidence of her latest win, she will take some stopping as she won 6-4 2-6 6-4.

Williams revealed she had to cope with a little off-court stress this week with her clothing line, and Sabalenka certainly kept the pressure up as the 22-year-old took the second set.

But Williams responded well to the seventh seed, who became the first player to take a set off the former world number one. Williams said she remained confident despite that setback.

"Like I said on the court, I just felt like even games that I lost, I was so close to winning. Not all games, but probably most of those games," she said. "I just needed to play better on the big points.  I knew that I could. I still hadn't reached my peak. I was like, 'Okay, Serena, you got this, just keep going.'"

OSAKA RELEASES HER ANGER

Osaka was in a real spot of bother against Garbine Muguruza, but saved two match points.

The 2019 champion Osaka steadied herself and felt more composed after a brief show of frustration, as she struck the ground with her racquet.

Ultimately, she emerged a 4-6 6-4 7-5 victor, and Osaka felt letting frustration get the better of her for a moment helped her cause.

"On the first match point, I was just thinking that I didn't hit a decent serve that entire game, so I should really focus on my serve," he said. "I feel like my serve stats were pretty good that set, so I was just telling myself to do better.

"Then on the second point, when the rally started, I just told myself not to push [the ball] but also don't do something crazy and make a really bad unforced error. I felt the entire match I was overthinking. There was a moment when I got angry and hit my racquet on the ground. I feel like I released a lot of the thoughts that I had. It just made me go more into instinct-based tennis."

She will face Hsieh next, the world number 71 having beaten Vondrousova – ranked 51 places higher – 6-4 6-2.