Jennifer Brady believes a two-week hard quarantine upon arriving in Australia helped her make a run to the semi-finals at Melbourne Park.

As one of the 72 Australian Open entrants that had potentially been exposed to COVID-19 on chartered flights to Melbourne, Brady was forced to stay in a hotel room for a fortnight ahead of the first grand slam of the year.

However, the 25-year-old booked her place in the final four on Wednesday by coming from behind to defeat Jessica Pegula 4-6 6-2 6-1 in an hour and 40 minutes on Rod Laver Arena.

While some players voiced their displeasure with the conditions they were faced with in self-isolation, Brady felt the period served her well.

"I was pretty much going non-stop since June of last year. I was playing World TeamTennis, then played tournaments in the US, then went over to Europe and was training in Europe till December," said Brady.

"I didn't have any weeks off. Mentally I was feeling a little bit fried, to be honest. I think I used that two weeks to kind of reset mentally and also physically, just give myself, my mind, my body a little bit of a rest.

"I would say I didn't really have high expectations on myself to do well. I came out of the quarantine, and then we were lucky enough to have a separate tournament for us who were in the hard lockdown. I was lucky to get a couple matches in there before starting here in the Australian Open."

The 22nd seed will take on Karolina Muchova in the last four, the Czech having stunned world number one Ash Barty earlier in the day. In the other half of the draw, Serena Williams will take on Naomi Osaka.

Brady hopes to get an opportunity to challenge herself against 39-year-old veteran Williams, who is chasing a record-equalling 24th major singles title.

"I think just being in the same draw as Serena is obviously... when she retires, if she retires, it's going to be something I'll be extremely grateful for. I hope I get to play her before she retires," said Brady.

"Yeah, I think she's the G.O.A.T. She's the greatest of all time and definitely will be the greatest of all time."

Brady made her first grand slam semi-final appearance at last year's US Open, when Williams and Osaka were also in the final four.

She suffered a three-set loss to Osaka on that occasion, but she is pleased to be performing on a par with the Japanese and Williams.

"I think it says a lot. They're obviously great, great tennis players, champions of the sport. To be categorised in the same group as them, I'll take that as an honour," said Brady.

"I think it's a huge achievement for me to make the semi-finals here. I look to make the finals, so we'll see."

Only Muchova stands between Brady and a first major final and fans will be able to attend after lockdown was lifted in Victoria, with a crowd of 7,477 – approximately 50 per cent capacity – allowed for each session.

Brady said of her next opponent: "She's crafty. She looks to move forward, has an all-court game. She's really athletic.

"I hope it will be a good, competitive match. Yeah, I'm looking forward to it."

Daniil Medvedev secured his first Australian Open semi-final berth after continuing his domination of fellow Russian Andrey Rublev in straight sets.

Medvedev starred in the Melbourne heat as countryman Rublev faded, winning 7-5 6-3 6-2 on Wednesday to reach his third grand slam semi-final, equalling Alex Metreveli for third place on the Open Era list for most major semis by a Russian man.

World number four Medvedev – the fifth Russian man to reach the Australian Open semis in the Open Era, after Metreveli (1972), Yevgeny Kafelnikov (1999-2000), Marat Safin (2002, 2004-05) and Aslan Karatsev (2021) – will face either 20-time slam champion Rafael Nadal or Stefanos Tsitsipas for a spot in the decider.

Medvedev and Rublev were meeting for the fourth time on the ATP Tour – their second in a grand slam quarter-final, with the former winning all previous meetings in straight sets. 

Runner-up at the 2019 US Open, Medvedev had a glimpse on Rublev's serve before breaking in the sixth game for a 4-2 lead, only to hand the break straight back to his countryman.

The tense battle continued behind closed doors on Rod Laver Arena as a tie-break loomed large, until Medvedev closed out the 46-minute set on Rublev's serve.

It was a similar theme in the second set, with little separating the two Russian hopefuls under the warm Melbourne sun.

Rublev, who won five ATP Tour titles last year – more than any other player, while earning a joint-best 41 wins in 2020 alongside world number one Novak Djokovic, continued to take the match to Medvedev.

Three break-point chances came Rublev's way in the seventh game, but he was unable to convert and Medvedev made him pay as the world number four broke the very next game before earning a two-sets-to-love lead.

Rublev – eyeing his first slam semi – deteriorated in the warm conditions, often hunched over between points while trying to keep cool in the shade, as Medvedev cruised.

Data Slam: Medvedev extends streak
There is no stopping Medvedev at the moment after he extended his winning streak to 19 matches, already a career-best run – dating back to the Vienna Open last October.

WINNERS/UNFORCED ERRORS
Medvedev – 30/33
Rublev – 20/39

ACES/DOUBLE FAULTS
Medvedev – 14/4
Rublev – 8/3

BREAK POINTS WON
Medvedev – 5/11
Rublev – 1/5

Sofia Kenin revealed she had her appendix removed after being diagnosed with acute appendicitis following her shock Australian Open exit.

Australian Open champion in 2020, Kenin was dethroned in the opening week of the grand slam at Melbourne Park, where she was stunned by Kaia Kanepi in the second round last Thursday.

American star Kenin – who suffered her earliest major exit since Wimbledon in 2019 – revealed via social media on Wednesday that she had an operation in Melbourne.

"Hey guys! I want to share with you what happened to me a few days ago," Kenin said via Twitter.

"I went to the tournament physician office on Monday, February 15th with acute abdominal pain. I was evaluated by the tournament physician and referred to the hospital for further evaluation.

"Acute appendicitis was diagnosed following the completion of my CT scan. I had to have surgery and had my appendix removed on Monday, February 15, at Epworth Hospital Richmond. 

"I want to thank everyone at Epworth Hospital Richmond for taking good care of me!"

World number one Ash Barty refused to criticise Karolina Muchova's reasoning for a medical timeout after she was surprisingly beaten in the Australian Open quarter-finals.

Barty's bid to become the first Australian woman to win the Melbourne grand slam since 1978 came to a shock end on Wednesday, upstaged by 25th seed Muchova 1-6 6-3 6-2.

Winner of the 2019 French Open, Barty raced through the opening set in 24 minutes and led 2-1 in the second before Muchova requested an off-court medical timeout on Rod Laver Arena.

It was a turning point, Muchova returning reinvigorated as the unheralded Czech reached her maiden major semi-final in remarkable fashion, with the 24-year-old revealing during her on-court interview, "I was a bit lost [gestures at head] on the court and my head was spinning so I took a break. It helped me.

"It was more they just checked my pressure because I was a bit lost. I was spinning. So they cooled me down a bit with ice and it helped me."

Asked about Muchova's actions, Barty told reporters: "It's within the rules. She's within her rights to take that time. If she wasn't within the rules, the physios and the doctors would have said so. That's the laws of our game, is that we have those medical timeouts for cases that are needed. Obviously she needed that today. Completely within the rules for her to take that.

"From my point of view, I've played a lot of matches where there have been medical timeouts. I've taken medical timeouts myself before, so that shouldn't be a massive turning point in the match. I was disappointed that I let that become a turning point. I'm experienced enough now to be able to deal with that. It's a disappointment today without a doubt. But we learn and we move on."

Barty added: "I would have liked to have just been a little bit sharper the next game. Started well with the first point, just made a couple loose errors in that game. I think for the rest of the set, that was the story, it was just over and over-made. Probably pressed a little bit trying to be overly aggressive.

"Had some break points, I think it was that three-all, that was probably a bit of a critical game in the momentum there for the second set. Just disappointed with the fact that I wasn't able to bring the match back on my terms after she took that break."

"I didn't hear what she said when she called for the trainer," Barty continued. "That's not my decision. When you call for the trainer, you obviously tell the umpire what the reason is. And then the doctor and physios come out and assess it. That's within the rules. For me, that's not really my decision and not my concern what she took the medical for.

"Obviously there are rules when we go off the court for whatever areas you're getting treated because that's quite normal. But, yeah, that's not really my decision to make on whether or what her medical condition was or what the timeout was for."

Brady, who tallied 31 unforced errors in the final two sets having only managed six in the first, said: "It's heartbreaking, of course. But will it deter me, will it ruin the fact we've had a really successful start to our season? Absolutely not.

"The sun will come up tomorrow. We go about our work again. You're either winning or you're learning. I think today is a massive learning curve for me, for Tyz [coach Craig Tyzzer], my team as well. We take the positives out of it, without doubt and don't let this particular match, this particular hour of tennis deter us from what we're trying to do."

Karolina Muchova completed a stunning comeback to upset world number one Ash Barty 1-6 6-3 6-2 in the Australian Open quarter-finals. 

Leading by a set and 2-0 in the second, Barty looked on track to reach back-to-back semi-finals at Melbourne Park, where she was bidding to become the first Australian woman to advance to the final since 1980 and first to lift the trophy since 1978.

But Czech 25th seed Muchova spoiled the 'Barty party' on Rod Laver Arena as her star opponent – unable to stop the rot – sensationally crashed out on Wednesday.

Muchova, whose only previous win against a top-five player came against Karolina Pliskova at Wimbledon two years ago, will contest her maiden major semi-final as either Jennifer Brady or Jessica Pegula await.

Played behind closed doors on the final day of a five-day state-wide lockdown in Victoria, Barty initially showed no mercy in warm and sunny conditions midweek.

Barty, who had lost the second-fewest games (20) en route to the last eight, raced out to a 5-0 lead in just 16 minutes – Muchova managing to avoid a first-set bagel in the only positive in an otherwise forgettable start.

Winner of the 2019 French Open, Barty only dropped three points on first serve, while she won 90 her cent of her second serves – finishing a lopsided first set with six winners and just as many unforced errors.

Progression to the semis appeared to be a foregone conclusion as Barty led and Muchova required a medical timeout away from the court at the end of the third game of the second set.

But Muchova emerged a new player, with Barty fading dramatically after everything she touched had turned to gold in the opening set.

Barty's unforced error count ballooned out to 19 as Muchova enjoyed great success on second serve, winning 12 of 15 points, while the former – who did not face a break point in the first set – only managed four of 15 and served three double faults.

Muchova continued her red-hot form in the deciding set - breaking in the opening game before saving a pair of break points to consolidate and she did not look back as she caused a boilover, which was sealed with an ace.

Data Slam: ​Barty loses her way
Unstoppable in a 24-minute first set, Barty crashed back down to earth thereafter. She missed routine shots consistently, with 31 unforced errors in the remaining two sets contributing to her demise.

WINNERS/UNFORCED ERRORS
Barty – 21/37
Muchova – 17/33

ACES/DOUBLE FAULTS
Barty – 3/3
Muchova – 2/3

BREAK POINTS WON
Barty – 3/13
Muchova – 4/11

Australian Open fans are set to return to Melbourne Park from Thursday after the Victorian government confirmed the lifting of restrictions following a five-day lockdown amid the coronavirus pandemic.

While the number of supporters set to attend remains unknown, fans will be back in their seats for the beginning of the Australian Open semi-finals, with record-chasing Serena Williams set to face three-time grand slam champion Naomi Osaka in Melbourne.

Defending men's champion Novak Djokovic will play the tournament’s surprise package, Russian qualifier Aslan Karatsev - who is the first player to reach a semi-final on their grand slam debut.

Djokovic was on court when the lockdown came into effect last Friday, with the five-day "circuit-breaker" designed to control an outbreak of the UK coronavirus strain.

Part of the third round, the fourth round and quarter-finals of singles action were played behind closed doors after a series of outbreaks in Victoria.

The state has recorded 12 more active cases since the lockdown was implemented but, with none discovered in the past 24 hours, Victorian premier Daniel Andrews announced restrictions will be eased.

"I'm very, very pleased to announce that the restrictions will come off, almost all of them, at midnight tonight," Andrews told reporters on Wednesday.

"From 11:59pm [Wednesday local time], the restrictions will be dropped [but] masks will be required indoors and outdoors when you can't socially distance."

The stage-four restrictions meant residents could not leave their homes for any other reason than work, shopping for groceries, exercise or the giving or receiving of medial care.

This year's delayed Australian Open has had crowds capped at 30,000 per day with original COVID-19 restrictions, but new limits are yet to be determined for the rest of the tournament.

"There will be meetings this afternoon [to determine] what is a safe number," Andrews said.

"They already were reduced, they may have to be reduced further, but that matter will be resolved in the next few hours."

Novak Djokovic lost his temper but refused to let the prospect of Australian Open glory slip away as he edged out Alexander Zverev to reach the semi-finals.

The world number one destroyed a racket when trailing 3-1 in the third set, after he and Zverev split the opening two sets, and it was one of a number of moments when the Serbian showed heightened volatility during a 6-7 (6-8) 6-2 6-4 7-6 (8-6) win.

Still bothered by an abdominal problem that he sustained in the third round, Djokovic nevertheless strides on and will face Russian qualifier Aslan Karatsev for a place in the final.

Zverev, who played in a bright yellow headband and vest top, with a gold medallion hanging from his neck, will look back on an opportunity missed.

As well as that third-set lead, Zverev was also up a break at the start of the fourth, but the US Open runner-up lacked the composure to convert those hard-earned positions.

If Djokovic's racket-smashing was a tactical move designed to gee himself up and distract Zverev, then it worked a treat.

A nip-and-tuck opener had gone the way of German world number seven Zverev, who then made a wretched start to the second set and was 4-0 behind in the blink of an eye.

Just as momentum began to swing back Zverev's way in the third, Djokovic went into his rage, with a ball girl summoned to clear up the mess the 33-year-old created.

Back came Djokovic as double faults began to leak from Zverev's racket, and soon they were into a fourth set.

Zverev led 3-0 but Djokovic was not going away, seizing on mistakes from an opponent who by the end of the second tie-break of the match could only wonder what might have been.

An ace from Djokovic finished off the contest. After eight titles at Melbourne Park, a hunger for more continues to define his every performance in Australia.

"Emotionally I feel a little bit drained. We pushed each other to the limit," Djokovic said in his on-court interview.

"Other than in the second set I started pretty poorly in all the other three sets. I lost my service very early in the first, third and fourth and allowed him to swing through the ball a bit more, but I regained my focus.

"I broke that racket and things started to shift a little bit for me in a positive direction."

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."

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]."

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.

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."

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