It remains to be seen whether Serena Williams returns to contest the Australian Open in 2022 but amid long-term doubts, Naomi Osaka said "I want her to play forever".

Williams' long-standing bid to equal Margaret Court's record of 24 grand slam titles was put on hold by three-time major champion Osaka, who overpowered the American superstar 6-3 6-4 in the blockbuster Australian Open semi-final.

Not since claiming the 2017 Australian Open trophy has Williams celebrated a slam crown, and the 39-year-old is not getting any younger as she faded into the Melbourne shadows on Thursday.

Williams broke down in tears and cut short her news conference post-match, having been involved in an emotional moment on Rod Laver Arena, where the seven-time Australian Open champion held her hand on her chest and waved to the crowd.

Asked what it means to face Williams as the clock ticks on a legendary career, Osaka – who topped the veteran in the 2018 US Open final – told reporters: "It definitely means a lot.

"Every time I play her, I feel like it's something I'll definitely remember a lot.

"I don't know, it's kind of sad when you say it like that because for me, I want her to play forever. That's the little kid in me."

Japanese star and third seed Osaka will now face Jennifer Brady in Saturday's final as she eyes her second Australian Open crown.

Osaka has gone on to win the title each time after advancing past the round of 16 at a slam – 2018 US Open, 2019 Australian Open and 2020 US Open, while she is in the midst of a 20-match winning streak.

Asked what makes her so hard to beat in finals, Osaka added: "For me, I have this mentality that people don't remember the runners-up. You might, but the winner's name is the one that's engraved.

"I think I fight the hardest in the finals. I think that's where you sort of set yourself apart. It's the other person who won as many matches as you did. It's something that I think, it's like the biggest fight."

Jennifer Brady will contest her first grand slam final after outlasting Karolina Muchova at the Australian Open.

A beaten semi-finalist at last year's US Open, American Brady took down fellow seed Muchova 6-4 3-6 6-4 in Melbourne on Thursday.

In a nervy finish, Brady wasted four match points before converting the fifth to secure a showdown with former world number one and three-time slam champion Naomi Osaka in Saturday's decider.

Brady (26) had dropped the fewest games en route to the semis and the 22nd seed looked like the player to beat in the opening set on Rod Laver Arena.

Despite Muchova recovering from a slow start to level the set at 2-2, Brady was not to be denied behind a strong first serve, even though her unforced-error tally reached 17 compared to just eight on her opponent's racquet.

Just like she did when upstaging world number one Ash Barty in the quarter-finals, 25th seed Muchova composed herself against the high-octane Brady.

Settling into a rhythm, Muchova was almost flawless in the second set, which only featured once unforced error, while the Czech won all of her second-serve points as she only dropped one point on first serve.

Muchova's measured aggression troubled Brady as the semi-final clash headed to a tense decider.

But Brady managed to slow down and settle back into her stride, an early break securing the advantage that the 25-year-old never relinquished in an engrossing finish.

Data Slam: ​Another finals debutant
Brady is the seventh woman to make her debut in a grand slam final in the past nine majors, after Osaka (won 2018 US Open), Barty (won 2019 French Open), Marketa Vondrousova (lost 2019 French Open), Bianca Andreescu (won 2019 US Open), Sofia Kenin (won 2020 Australian Open) and Iga Swiatek (won 2020 Roland Garros).

WINNERS/UNFORCED ERRORS
Brady – 20/38
Muchova – 21/29

ACES/DOUBLE FAULTS
Brady – 8/2
Muchova – 1/2

BREAK POINTS WON
Brady – 3/3
Muchova – 3/7

Serena Williams refused to confirm whether she made her last Australian Open appearance after breaking down in tears and leaving her news conference following a semi-final defeat to Naomi Osaka.

Bidding to equal Margaret Court's record of 24 grand slam titles – having last won a major in 2017 – Williams was overpowered 6-3 6-4 by third seed Osaka in Melbourne on Thursday.

It was Williams' first semi-final defeat at the Australian Open following eight consecutive victories in the final four of the year's opening slam.

The 39-year-old American star cut an emotional figure afterwards on Rod Laver Arena, where she held her hand on her chest and waved to the crowd after fans were allowed to attend following a five-day coronavirus shutdown.

Asked about the moment, seven-time Australian Open champion Williams told reporters: "The Aussie crowd is so amazing, so it was nice to see."

When pressed if it was a Melbourne farewell, Williams replied: "I don't know. If I ever say farewell, I wouldn't tell anyone."

A tearful Williams then suddenly ended her news conference after being asked about the match.

Williams was visibly and vocally frustrated against Osaka after seeing an early 2-0 lead slip.

Osaka reeled off five consecutive games and six of the next seven to close out the set before taking complete control against the former world number one.

Williams finished with 24 unforced errors against the three-time slam champion and 2019 Australian Open winner.

At the start of her post-match duties, Williams said: "I wouldn't say I was nervous. The difference today was errors. I made so many errors today.

"Honestly, it was opportunities where I could have won. I could have been up five-love. I just made so many errors."

"I felt like I was hitting well," Williams added. "I was hitting well this whole tournament. Even the first couple games I played well. Even then I had so many opportunities.

"I don't know. Just made too many mistakes there, easy mistakes. Not like I was on the run or anything, they were just easy, easy mistakes."

Serena Williams' quest for a record-equalling 24th grand slam title has been delayed again after being overpowered 6-3 6-4 by third seed Naomi Osaka in the Australian Open semi-finals.

Stuck on 23 slam championships since reigning supreme at Melbourne Park in 2017, Williams was hoping to move within a step of matching Margaret Court's record.

But the 39-year-old former world number one was taken down by three-time major champion Osaka in a blockbuster battle of the big hitters on Thursday.

Japanese star Osaka will now face either Jennifer Brady or Karolina Muchova in Saturday's final as she eyes her second Australian Open crown.

Osaka – the youngest player remaining in the draw – initially struggled under the beaming Melbourne sun as fans returned to Rod Laver Arena following a five-day state-wide lockdown after a coronavirus outbreak.

She was in all sorts, struggling on serve and tallying five unforced errors through two forgettable games as Williams raced out to a 2-0 lead.

Osaka – boasting a 3-0 record in grand slam semis – faced a 30-40 deficit and potential 0-3 hole before digging deep to hold for the first time.

It proved to be a turning point for Osaka, who went on a roll by reeling off five successive games and six of the next seven to take complete control.

The tables turned on Williams, who saw her unforced-error count balloon out to 16 while only hitting four winners in the opening set.

Williams – the oldest woman to reach the semis in Melbourne in the Open Era – carried a flawless Australian Open semi-final record into the contest, having won all eight of her previous final-four showdowns.

But Williams cut a frustrated figure at the start of the second set as she yelled at herself "make a shot" amid her demise – Osaka breaking in the first game before consolidating.

However Osaka, who has gone on to win the title each time after advancing past the round of 16 at a slam – 2018 US Open, 2019 Australian Open and 2020 US Open, lost her way when serving at 4-3 as three double faults saw her broken by Williams.

Williams, beaten by Osaka in an infamous US Open final three years ago, regifted the compliment the very next game, Osaka hitting three stunning winners to break to love before sealing her place in the women's decider.

Data slam: Osaka stays hot
She has now won 20 consecutive matches since losing while on Fed Cup duty for Japan last February. A 21st successive victory would yield a fourth slam triumph.

WINNERS/UNFORCED ERRORS
Williams – 12/24
Osaka – 20/21

ACES/DOUBLE FAULTS
Williams – 3/1
Osaka – 6/8

BREAK POINTS WON
Williams – 2/7
Osaka – 4/4

Rafael Nadal insists he was not struggling with injury as he crashed out of the Australian Open but acknowledged a lack of match practice could have contributed to his quarter-final collapse against Stefanos Tsitsipas.

The 20-time grand slam champion was dealing with a back issue at the start of the tournament, although he managed to advance to the last eight without dropping a set.

That impressive run appeared set to continue as Nadal won the opening two sets against fifth seed Tsitsipas, only for the match to turn on its head after a tie-break in the third

Tsitsipas emerged a 3-6 2-6 7-6 (7-4) 6-4 7-5 winner after just over four hours, becoming only the second player – after Fabio Fognini – to triumph from two sets down against Nadal at a major.

Post-match questions put to Nadal predictably centred on the potential impact of his back woe, but he insisted there was no physical pain on Wednesday.

However, reflecting on "just another story in my tennis career", the Spaniard repeatedly referred to the difficulty of preparing for a tournament amid such problems.

"I think I was in great condition before here," he said. "Then I've been a bit unfortunate for what happened for 20 days, and then I fight back to play, I think, decent tennis.

"Today wasn't enough. It was close, just that's tennis. That's all. That's the sport. One player wins; the other loses.

"Today I lost, so the only thing that I can do is try to be better next time, and today congratulate him."

Claiming the key was instead two costly mini-breaks in the breaker, Nadal added: "I am not complaining much.

"I think physically, it has been a very humid day out there. Physically I was not fantastic but not bad, you know? I was able to fight until the end, and that's it.

"The whole issue is I missed an easy smash at the beginning of the third, an easy forehand with 2-1 in the tie-break, and then another smash in that tie-break.

"That tie-break I made a couple of mistakes that I can't make to win the match. He played well then later. Well done."

Nadal was chasing a record-breaking 21st major championship, yet only one of those triumphs has come in Melbourne – back in 2009.

The 34-year-old has lost four finals, as well as regularly dealing with injury concerns at the first slam of the season.

But asked if he felt "cursed", he responded firmly: "No. No, no, no. That's sport. Sometimes things go well; other times things goes worse.

"Unfortunately for me, in this tournament, I had more injuries than in the others. Then matches that you lose like today against one of the best players of the world is something that happens.

"No, no, no. Not at all feeling unlucky for me and not at all complaining about my luck here in Australia.

"Everyone has what we deserve. Tennis isn't a sport that is fair. I have what I deserved in my career, and over here in Australia I had chances, but I was not able to convert it. That's all. I didn't deserve more."

Use of the word "unlucky" brought a similar response, as Nadal insisted he was not looking for excuses.

"We can find excuses or reasons or maybe this quarantine that we need to be more time in the room than usual, yes, maybe," he said. "But I am not the guy that is going to find excuses on that or going to complain about what happened, no.

"Just accept. I never considered myself an unlucky person at all. It doesn't matter the injuries that I had. I think I am very lucky person.

"The only thing that I can do is just keep going. I put myself in a position, even with the challenges that I faced, that I was in quarter-finals with two sets up, close to being in the semi-finals.

"So, it has been a chance lost, yes, but life continues. I hope to keep having chances. Well, I'm going to keep fighting for it."

Stefanos Tsitsipas struggled to explain how he pulled off a remarkable turnaround against Rafael Nadal to reach the last four of the Australian Open.

The fifth seed had only once before beaten Nadal and was facing a seventh career defeat to the 20-time grand slam champion as he fell two sets behind on Rod Laver Arena.

Instead, Tsitsipas rallied after a third-set tie-break to triumph 3-6 2-6 7-6 (7-4) 6-4 7-5 and advance to a semi-final against Daniil Medvedev.

The Greek joined Fabio Fognini, at the 2015 US Open, as the only players to overturn a two-set deficit to beat Nadal at a major.

Victory had seemed particularly remote as Tsitsipas struggled to make any inroads on Nadal's serve. He won only 10 receiving points across the first two sets - two of those coming courtesy of double faults - and had to wait until the final game before the breaker in the third to add an 11th.

Then, to the victor's bemusement, the match turned, ending Nadal's run of 35 consecutive set wins at grand slams.

"I have no words to describe what has just happened on the court," Tsitsipas said. "My tennis speaks for itself.

"It's an unbelievable feeling to fight at such a high level and leave it out on the court. I started very nervously.

"I don't know what happened after the third set. I flew like a bird and everything worked for me."

Tsitsipas, who made just four unforced errors in the pivotal third set, added: "I focused on staying calm and holding my nerves today. I have failed to do so in some of my matches.

"I stayed calm in the tight moments and I kept everything to myself. I am really happy with the attitude that I showed on the court."

Now Tsitsipas must take on another player he has only previously defeated once, although that win came in his most recent meeting with Medvedev in 2019.

"He plays very well and has been very consistent, with lots of consecutive wins," Tsitsipas said. "I need to recover and have a good ice bath.

"I am looking forward to the match and each match I play here is an opportunity to play my best tennis. It will be amazing to see the crowds again."

Rafael Nadal suffered a remarkable collapse to exit the Australian Open at the quarter-final stage despite earlier leading Stefanos Tsitsipas by two sets.

Only once in Nadal's grand slam career had he previously let a two-set lead slip and such a slump appeared entirely improbable as he dominated Tsitsipas on Rod Laver Arena.

But the 20-time major champion, chasing a record-breaking 21st title, struggled to recover his momentum after dropping a set for the first time in the tournament when the third went to a tie-break.

The courageous Tsitsipas grew in confidence and landed a momentous second career win over Nadal to reach a third slam semi after a four-hour 3-6 2-6 7-6 (7-4) 6-4 7-5 epic.

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."