Novak Djokovic's hopes of becoming the first man to win a calendar Golden Slam were crushed by a semi-final defeat to Alexander Zverev at the Tokyo Olympics.

From a set and a break up, Djokovic dropped a staggering eight games in a row on his way to a 1-6 6-3 6-1 loss.

The 34-year-old Serbian had been unsure about coming to the Games but was swayed by the pride he takes in representing his country and the tantalising opportunity to add a gold medal to a potential clean sweep of the grand slams.

He has already won the Australian Open, French Open and Wimbledon, and will head to the US Open in August as a heavy favourite regardless of this setback.

But this was just not Djokovic's day, despite him making a whirlwind start and dominating until the point he broke to lead 3-2 in the second set. From there, Zverev seized control. 

When Djokovic volleyed into the net to make it 3-3, dropping serve for the first time in the match, it looked like just a minor stumble.

Yet suddenly he was struggling for form and did not win another game until he was already 4-0 behind in the deciding set.

Zverev was playing blindingly brilliant tennis and was proving obdurate too, saving four break points in the second game of the third set.

He clinched victory with a blazing backhand winner, and goes on to face Russian Karen Khachanov in the final.

The result means Djokovic, like Roger Federer, seems fated never to win the Olympic singles gold medal. And it leaves Steffi Graf as the only player to ever win a calendar Golden Slam, having done so in 1988 when she added the Seoul Olympics title to her haul of majors.

Russian Olympic Committee's Khachanov fended off Spain's Pablo Carreno Busta with some ease in the first semi-final, with the world number 25 sweeping to a 6-3 6-3 victory in an hour and 19 minutes.

He won 26 of 28 points on first serve to freeze out Carreno Busta, who had only one break point all match and could not take that opportunity.

"It's just a pure happiness, a pleasure to be here to live those moments, these kind of memories will stay forever," Khachanov said.

Khachanov delivered a rock solid display, with his serve and forehand at their best, barely giving his opponent a sniff of an opportunity as the Moscow-born 25-year-old established a firm grip.

"That's the way I prepared, against every opponent you play a little bit differently," Khachanov said. "The final will be another story, another match, another day. I hope it will be the same."

Carreno Busta, who will face Djokovic for the bronze medal, said: "It was not the best match I have played, but Karen was unbelievable today, playing very aggressive and serving really good."

Cameron Norrie breezed past Nick Kyrgios and John Isner downed countryman Jack Sock to advance to the quarter-finals at the Atlanta Open on Thursday. 

The third-seeded Norrie defeated Kyrgios 6-1 6-4 in less than an hour as he tries for a second consecutive title after collecting his first ATP Tour championship at Los Cabos last week. 

The former University of Georgia star Isner, a five-time champion in Atlanta, beat Sock 7-6 (8-6) 6-4 despite serving only 13 aces after hitting 36 in his previous match. 

Second-seeded Jannik Sinner fell 7-6 (9-7) 6-4 to Australian qualifier Christopher O'Connell, leaving the tournament without its top two seeds after Milos Raonic was upset by Brandon Nakashima on Wednesday. 

O'Connell, ranked 132 in the world to Sinner's 23, had not won a main-draw match this year before defeating Denis Kudla in the opening round and will now face Isner in the quarters.

Norrie will meet Emil Ruusuvuori, who advanced when Benoit Paire retired down 3-0 in the third set after the pair had split the first two sets 4-6 6-4. 

Ruusuvuori is into his second career ATP quarter-final after making it to the semis at Nur-Sultan last year. 

Casper Ruud survived a scare as he progressed to the Generali Open semi-finals with a 3-6 7-6 (7-5) 6-1 victory over Mikael Ymer.

World number 14 Ruud is targeting a third successive ATP title, having also captured the Swedish Open and Swiss Open earlier this month.

It has been a timely return to form for the Norwegian, who suffered a shock defeat to Australia's Jordan Thompson at Wimbledon at the end of June.

Although he was in danger of seeing his nine-match winning streak come to an end in Kitzbuhel, after losing the opening set against Swedish opponent Ymer.

Ruud, who also triumphed at the Geneva Open in May, was then taken to a tie-break in the second ser by the world number 99, but held his nerve to tee up a decider.

It was one-way traffic from there with the 22-year-old dominating play to set up a last-four clash with Arthur Rinderknech, who hit five aces as he overcame third seed Filip Krajinovic 6-4 6-1.

Meanwhile, Daniel Altmaier's place in the semi-finals was secured with a 6-1 6-7 (5-7) 6-3 win over Gianluca Mager.

The world number 135, who reached the fourth round of last year's French Open, will play Pedro Martinez in the semi-finals after the Spaniard saw off Jozef Kovalik 6-2 6-2.

Friday sees the start of the Olympic athletics schedule and the first tennis medals will be won in Tokyo.

The men's 10,000 metres final will be staged on the first day of track and field action at the Olympic Stadium.

There will be an all-Croatia men's doubles gold medal match at the Ariake Tennis Park, plus no doubt more drama to come in the pool.

Stats Perform picks out some of the standout events to look forward to.

CHEPTEGEI FAVOURITE FOR FIRST TRACK GOLD

Joshua Cheptegei and Jacob Kiplimo both have the chance to become the first athlete from Uganda to win an Olympic gold medal in the men's 10,000m final.

Cheptegei, the 2019 world champion, is well fancied in the last event on the track on Friday, while his compatriot Kiplimo could become the youngest man to be crowned champion at the distance at the age of 20 years and 258 days.

Yomif Kejelcha of Ethiopia and Canadian Mohammed Ahmed also have high hopes of making it onto the podium. 

Other events to look out for are the start of the women's 100m, men's 400m hurdles and men's high jump, along with the women's 800m and women's triple jump.

CROATIA GUARANTEED DOUBLES GOLD

One guarantee on Friday is that Croatia will add a gold and silver medal to their tally at the Tokyo Games.

Marin Cilic and Ivan Dodig will face compatriots Nikola Mektic and Mate Pavic in the gold medal match in the men's doubles final.

The men's singles semi-finals will also take place, with Novak Djokovic, chasing a Golden Slam this year, up against Germany's Alexander Zverev.

Karen Khachanov of the Russian Olympic Committee will do battle with Spaniard Pablo Carreno Busta to find out who will make it through from the other half of the draw.

HIGH HOPES FOR AUSTRALIAN DUO

Emma McKeon and Cate Campbell could make it an Australia one-two in the women's 100m freestyle final.

McKeon set a new Olympic record of 52.13 seconds on Wednesday and will go out in lane four next to her dangerous compatriot Campbell.

That is one of four finals on Friday, with Tatjana Schoenmaker of South Africa expected to take some stopping in the 200m breaststroke final after clocking an Olympic record time of 2:19.16 this week.

Medals will also be up for grabs in the men's 200m backstroke final and the men's 200m individual medley.

Sunisa Lee stepped up in the absence of Simone Biles to claim gold and maintain Team USA’s dominance in the women's gymnastics all-around event.

The 18-year-old became the sixth American woman to take the title – and fifth in a row – after beating Brazil's Rebeca Andrade and Angelina Melnikova to gold.

Despite withdrawing from the final to focus on her mental health, Biles was cheering on from the stands as her team-mate aimed to capitalise.

Lee was looking to continue her nation's impressive record in this event, which has seen triumph concurrently at both the Olympic Games and World Championships since 2010.

The teenager admitted she came close to quitting gymnastics following a difficult two years – both in and out of the gym.

Nevertheless, she duly delivered the goods by totalling 57.433 to take gold and edge out Andrade, who became the first Brazilian woman to claim an Olympic medal in artistic gymnastics.

"It feels crazy, it is so surreal. It's a dream come true," Lee said. "I don't even know what to say. It hasn't even sunk in. The past two years with COVID have been crazy. There was one point I wanted to quit. 

"To be here and to be an Olympic gold medallist is just crazy."

PATIENT FOX COMES GOOD

Australia's Jess Fox became the first women's canoe slalom (C1) Olympic gold medallist.

A multiple World champion, Olympic gold has eluded Fox over the years. She was a silver medallist at London in 2012, while she took home a bronze from Rio four years later.

However, her persistence finally paid off after posting a time of 105.04 seconds in the final, while Great Britain's Mallory Franklin and Andrea Herzog of Germany completed the podium.

"I can't believe it," said Fox, who also won bronze in the women's kayak earlier this week.

"I was dreaming of [a gold medal] and I really believed it was within me, but you never know what is going to happen at the Olympics.

"It is about holding your nerve and I probably didn't do that very well in the kayak a couple of days before, so it was hard to get to this point. But it has been incredible to do what I did today."

Novak Djokovic is growing in confidence after his bid to win a gold medal at the Olympic Games stayed on track on his "best day" of Tokyo 2020.

The Serbian cruised into the semi-finals of the singles tournament with an emphatic 6-2 6-0 win over home favourite Kei Nishikori of Japan, then teamed up with Nina Stojanovic to beat German pair Laura Siegemund and Kevin Krawietz in the mixed doubles quarter-finals.

World number one Djokovic, 34, is attempting to become the first man to win all four tennis singles grand slam titles and an Olympic gold in the same year.

He has already triumphed at the Australian Open, French Open and Wimbledon, leaving just Tokyo and the US Open to conquer.

Asked after his doubles win if this was the best year of his career, Djokovic replied: "I don't know. Today was the best day of this tournament because I've played my best tennis so far."

Those comments echoed his assessment of the Nishikori match, after which he said: "I'm very happy – my best performance in the tournament."

Djokovic said he "had an answer for everything [Nishikori] had" and now he will face Alexander Zverev.

Asked how confident he felt heading into the last four, the 20-time grand slam champion replied: "Very."

Djokovic was boosted by the later start times for his matches after the International Tennis Federation bowed to pressure from players complaining of the extreme heat and humidity at Ariake Tennis Park.

"It's great that we're playing in the afternoon hours, so we don't experience too much heat," Djokovic said.

"Although it's still very, very humid. It's a bit easier, more pleasant to play in the afternoon. It was fantastic. 

"Playing after 5[pm] is completely different.  Obviously, there is a little bit of a breeze, but still very, very humid, you sweat a lot, but you don't have the heat, you don't have the sun that, in combination with the humidity, is just brutal."

Novak Djokovic cruised through to the men's singles semi-finals after a commanding straight-sets victory over Kei Nishikori at the Ariake Tennis Park.

The world number one is yet to drop a set at the Tokyo Games after running out a 6-2 6-0 winner against home favourite Nishikori, who claimed bronze in Rio five years ago.

Having already won the Australian Open, French Open and Wimbledon this year, Djokovic is aiming to become the first male player of the Open era to complete the Golden Grand Slam.

Should he claim gold in Tokyo and go on to triumph at the US Open, he would become only the second player overall to achieve the feat, after Steffi Graf in 1988.

However, the Serbian has never reached an Olympic final – his best result coming in for the form of a bronze medal in Beijing.

"Matches are not getting easier, but my level of tennis is getting better and better," Djokovic told reporters after setting up a last-four tie with Alexander Zverev.

"I've done that many, many times in my career. I know that I'm the kind of player that the further the tournament goes, the better I'm feeling on the court.

"That's the case here, [it was] my best performance of the tournament tonight against a very good opponent."

DANIIL DUMPED OUT

Standing in the way of Djokovic and a shot at the gold medal is fourth seed Zverev.

The big-serving German saw off Jeremy Chardy 6-4 6-1 and like Djokovic is yet to drop a set at the tournament.

World number five Zverev, who hit 11 aces during the contest, broke early on the way to edging a closely fought opening set. The US Open finalist then went into overdrive with three breaks on the way to sealing the deal.

There was, however, no joy for second seed Daniil Medvedev, as he went down 2-6 6-7 (5-7) against Spain's Pablo Carreno Busta, who is looking to replicated Rafael Nadal's effort from 2008.

"Today, he could win a Masters easily, and yet he's never been in any final of those," the Russian said of his opponent.

"With the level he showed here today, he can get to the final of a Grand Slam easily. I couldn't play better than what I did today. It was not easy to play and I'm really disappointed with myself and for my country to lose in the quarters."

FROM RUSSIA WITH LOVE

Despite Medvedev's exit, Russia – or, at least, the Russian Olympic Committee – will be represented in the semi-finals by Karen Khachanov.

A quarter-finalist at Wimbledon earlier this month, the 12th seed built on his momentum by overcoming Ugo Humbert in three sets.

Khachanov took the opener on a tie-break but was pegged back by the Frenchman in the second as the contest went to a decider.

But he established early control by breaking to love in game four before holding out to prevail 7-6 (7-4) 4-6 6-3.

Marketa Vondrousova landed another huge scalp in the form of Elina Svitolina to book her place in the gold medal match at Tokyo 2020 against Belinda Bencic.

It has been a memorable week for Vondrousova, who knocked out cauldron-lighter and "face of the games" Naomi Osaka in round three.

One more hurdle still stands in her way in the form of ninth seed Bencic, who fought hard for a three-set triumph over Elena Rybakina.

VONDROUSOVA MARVELS AGAIN

Vondrousova has had a Games to remember and she was a 6-3 6-1 winner against heavily fancied fourth seed Svitolina, becoming the first female Czech to reach an Olympic singles final in the process.

It means the Czech Republic will have a women's singles competitor on the podium for the second straight Games after Petra Kvitova finished with bronze at Rio 2016.

Incredibly, Vondrousova did not even automatically qualify for these Games with Karolina Pliskova, Barbora Krejcikova, Kvitova and Karolina Muchova ahead of her in the qualifying pecking order.

Vondrousova opted to use her protected ranking, dating back to a wrist injury prior to the pandemic, meaning Muchova missed out. Though criticised at the time, she is the last of the four remaining.

TEARS FOR BENCIC

Switzerland has a proud history of tennis stars but neither the legendary Roger Federer nor the great Martina Hingis have won Olympic gold in a singles event. Bencic has the chance to do that, though.

She had to go the distance against Rybakina in a 7-6 (7-2) 4-6 6-3 victory, with Bencic fighting back from 5-2 down in the first set.

Eventually Bencic came through in two hours and 44 minutes and the tears poured as she made the final.

"My emotions right now... it's too high," Bencic told the ITF website. "To have a medal, it's the greatest thing. Even to be here as an athlete, in the Olympics, it's amazing."

It means Switzerland will medal for the fourth straight Games with Federer, Stan Wawrinka, Hingis and the recently retired Timea Bacsinszky all having medalled.

The last Swiss gold medallist was at Barcelona 1992 where Marc Rosset won the men's singles.

Elsewhere, singles world number one Ash Barty remains in the hunt for mixed doubles gold. She and partner John Peers defeated Greek pair Stefanos Tsitsipas and Maria Sakkari – winning on a 10-point tie-break after the first two sets were shared.

Top seed Milos Raonic saw his stay at the Atlanta Open come to an early end with a three-set defeat to American Brandon Nakashima on Wednesday. 

The 19-year-old Californian Nakashima, ranked 115th in the world, prevailed 5-7 6-3 7-6 (7-4) over world number 22 Raonic in their first meeting. 

The big-serving Canadian had 10 double faults to go with his 27 aces, while Nakashima did not commit one double fault and managed 13 aces. 

It was the latest in a string of recent wins over established players for Nakashima, who stunned Sam Querrey and John Isner last week at Los Cabos before falling to Cameron Norrie in the final. 

Nakashima next faces Australia's Jordan Thompson, who beat Peter Gojowczyk of Germany 7-6 (8-6) 6-4 to reach the quarter-finals. 

In the other half of the draw, fifth seed Taylor Fritz rallied to defeat fellow American Steve Johnson 6-7 (5-7) 6-4 6-1 in a rematch of a quarter-final at Los Cabos, also won by Fritz. 

Fritz will face countryman Reilly Opelka, who outlasted Bjorn Fratangelo 7-6 (7-3) 7-6 (7-4). The 6-foot-11 Opelka pounded 25 aces to just three double faults, winning 84 per cent of his service points. 

World number 16 Roberto Bautista Agut crashed out in the second round as the other favourites for the Generali Open battled through.

Bautista Agut lost the first set to Spanish compatriot Pablo Martinez in Kitzbuhel, Austria, and could not complete a comeback despite forcing a decider as he lost 6-4 6-7 (5-7) 7-5.

Top seed Casper Ruud, who won last week in Gstaad to claim his third ATP Tour crown of 2021 and fourth in total, came from 4-2 down in the first set to win 7-5 5-7 6-4 against Mario Vilella Martinez.

Third seed Filip Krajinovic survived a second-set scare to beat Carlos Taberner 6-3 2-6 6-4.

Arthur Rinderknech, who dispatched of fifth seed Federico Delbonis on Tuesday, awaits Krajinovic in the next round.

The other clash on Wednesday saw Sweden's Mikael Ymer cruise past home favourite Alexander Erler 6-2 6-3 to secure a quarter-final berth.

Ymer will now face the thankless task of challenging 22-year-old Ruud for a spot in the semi-finals.

Novak Djokovic has welcomed the International Tennis Federation's (ITF) decision to delay the start of matches until 3:00pm (local time) at the Tokyo Olympics on Thursday.

The world number one has cruised through to the quarter-finals, where he will meet home favourite Kei Nishikori, but he – along with many others – had complained of heat and humidity causing problems due to contests starting too early.

That decision has come after world number two Daniil Medvedev struggled with conditions as he was forced to use two medical timeouts on Wednesday to cope with the heat and subsequently asked chair umpire Carlos Ramos, per ESPN, "If I die, are you going to be responsible?"

The pushback now means the majority of the games in the closing stages will be played in slightly cooler conditions in order to protect player welfare amid growing health concerns.

Speaking after a 6-3 6-4 mixed doubles win with Nina Stojanovic against Brazil's Luisa Stefani and Marcelo Melo, the Serbian expressed gratitude for the ITF's decision, though he felt it should have come earlier.

"It was nice news to receive," Djokovic said. "It's better than starting at 11:00am. It's not just in my opinion. I've spoken to six out of eight quarter-finalists in men's singles and everyone is in favour of starting later because the conditions are really brutal.

"It's very good [news] because you don't want to see situations like what we saw today with Paula Badosa [who retired after the first set].

"I've played tennis now professionally for 20 years, and I've never faced these kind of conditions in my entire life on a consecutive daily basis.

"I did experience certain similar days, one day in Miami or New York, or sometimes it happens here and there, but it's one or two days, and then it passes. Here is every single day. So, it's really draining players' energy, and you just don't feel yourself."

After gymnast Simone Biles' withdrawal to protect her mental health, Djokovic outlined the pressures that come with professional sport, too.

"Pressure is a privilege, my friend. Without pressure, there is no professional sport," he continued.

"If you are aiming to be at the top of the game, you better start learning how to deal with pressure and how to cope with those moments on the court, but also off the court.

"I've developed the mechanism on how to deal with it in such a way that it will not pose a distraction to me. It will not wear me down. I feel I have enough experience to know myself how to step on the court and play my best tennis.”

Djokovic, who was unsure if he had ever played in an "official" mixed doubles competition, and Stojanovic will now face Germany's Laura Siegemund and Kevin Krawietz in the quarter-final.

Despite limited experience, the six-time Wimbledon winner enjoyed the outing and was surprised how quickly he and Stojanovic understood each other's games.

"We did not chat about the tactics too much," the 34-year-old added. "We know each other, but we've never really played in the opposite ends of the net, or the same side of the net, so it was amazing how well we clicked from the beginning."

Daniil Medvedev did not take kindly to a question over the controversy surrounding Russian athletes at the Tokyo Olympics after he battled through sweltering conditions to reach the quarter-finals.

Medvedev beat Italy's Fabio Fognini 6-2 3-6 6-2 on Wednesday in a match that was paused for 10 minutes due to on-court temperatures reaching 31 degrees Celsius, with humidity then adding to that.

The world number two had to receive medical attention on two occasions before he prevailed to tee up a last-eight tie with Pablo Carreno Busta of Spain.

Top seed Novak Djokovic continued his march towards the medal matches with a routine win over Alejandro Davidovich Fokina, though in the doubles, Andy Murray's hopes of winning a historic fourth Olympic prize were shattered.

MEDVDEV'S TEMPER FRAYS IN THE HEAT

It had already been a stressful day for Medvedev. The 25-year-old replied "I can finish the match but I can die. If I die, are you going to be responsible?" when asked by chair umpire Carlos Ramos whether he could carry on playing against Fognini following two medical timeouts. 

Medvedev's temper then boiled over in the media mixed zone when he was questioned over the contentious nature of Russian athletes competing at the Games.

The Russian flag is not represented in Tokyo due to sanctions against the country for state-sponsored doping offences. Russia is suspended from competing in global sporting events for two years – a ban that was reduced from an initial four-year punishment. Instead, athletes are competing under the banner of the Russian Olympic Committee (ROC).

Medvedev was asked if he feels the Russian athletes are "carrying a stigma of cheaters".

Seemingly misunderstanding the question, Medvedev hardly held back in his reaction, saying: "That's the first time in my life I’m not gonna answer a question, man. And you should be embarrassed of yourself."

Before leaving the room, Medvedev subsequently told the press officer: "I think you should [remove] him from either the Olympic Games, either the tennis tournament. I don't wanna see him again in my interviews. Thanks."

MURRAY'S PARIS PARTICIPATION IN DOUBT

There was to be no fairytale title tilt for former world number one Murray. He won gold in the singles in London and Rio, and also managed a silver medal at the 2012 Games in the mixed doubles, but he and Joe Sailsbury suffered a defeat to Croatian pair Marin Cilic and Ivan Dodig in the quarter-finals.

The British pair won the first set but failed to make their advantage count, with Croatia's duo coming back to win 4-6 7-6 (7-2) 10-7.

Murray will be 37 by the time the Paris Games come around, and as he continues to carefully manage his return from hip surgery, the Scot could well have made his Olympic farewell.

"I don't know. I don't know if I'll get the opportunity to play [in the Olympics] again," he conceded.

"I love every minute of playing the Olympics. I wish that today would have gone differently. I had another chance with Joe to win a medal. We were so close and that is just disappointing. There was some stuff I wish I could have done at the end of the match to try and help out more. But yeah, very disappointing."

MIXED BAG FOR TSITSIPAS

While Medvedev, Djokovic and Alexander Zverev all progressed into the last eight in the singles, there was no place for Stefanos Tsitsipas, whose hopes were ended by Ugo Humbert.

The Greek world number four suffered a seemingly innocuous leg injury in the second set tie-break and failed to recover in the decider as Frenchman Humbert claimed the biggest win of his career.

However, Tsitsipas was swiftly back on court to play in the mixed doubles alongside partner Maria Sakkari, and the duo claimed a comfortable 6-3 6-4 victory over Canada's Gabriela Dabrowski and Felix Auger-Aliassime.

Asked after that win to discuss what went wrong in his earlier defeat, Tsitsipas replied: "I figured out a few things later during the match, like really, really late. 

"I think if I've had the same mindset or the same attitude, same vision that I had towards the very end of the match, I think things would have gone much, much smoother and better for me. It's something that I learned."

He also confirmed his injury was "nothing serious."

DJOKOVIC ON A ROLL

As expected, Djokovic is one win away from a shot at a medal in the singles, and he then followed up his victory over Davidovich Fokina by combining with Nina Stojanovic in the mixed doubles.

The Serbian pair beat Marcelo Melo and Luisa Stefani of Brazil 6-3 6-4 in just 70 minutes to book their place in the next round.

Djokovic will have the host nation against him in his next match, however, as he takes on Kei Nishikori, who is Japan's only hope of a singles medal after Naomi Osaka's exit.

The International Tennis Federation (ITF) has confirmed matches at the Tokyo Olympics will now start later in the day after concerns over player health and welfare.

World numbers one and two Novak Djokovic and Daniil Medvedev have been among the players to complain about games starting too early in the day, citing the heat and humidity at Ariake Tennis Park as a major issue.

Indeed, on Wednesday, 25-year-old Medvedev struggled with the conditions as he battled to a 6-2 3-6 6-2 win over Fabio Fognini.

Despite being allowed 10 minutes off court at one stage, Medvedev was in visible discomfort during the last-16 tie, and had two medical timeouts before being asked by chair umpire Carlos Ramos whether he could continue.

"I can finish the match but I can die," the Russian replied to Ramos, per ESPN. "If I die, are you going to be responsible?"

The 72 per cent humidity meant 31 degrees Celsius felt like 37 degrees Celsius on the heat index. Medvedev was not the only player to suffer on Wednesday, with Paula Badosa having to be taken from the court in a wheelchair as she retired against Marketa Vondrousova due to heatstroke.

Earlier in the week, Medvedev had questioned the approach of starting matches in the late morning, while top seed Djokovic suggested scheduling the first games for 15:00 local time.

The ITF has now agreed, with start times pushed back to 15:00, meaning the majority of matches in the closing stages of the Olympic tennis will be played during the slightly cooler evening hours.

"In the interests of player health and welfare and following extensive consultation, the ITF has announced a change of schedule due to the increasing heat and humidity currently being experienced in Tokyo," an ITF statement read.

"The decision to start matches at 3pm JST from Thursday is possible due to the outcomes of today’s matches across the five competitons being staged and the size of the player field.

"[The decision] is designed to further safeguard player health."

Paula Badosa was forced to withdraw from her quarter-final against Marketa Vondrousova and taken from the court on a wheelchair after suffering from heatstroke at Tokyo 2020.

Tuesday saw heavy downpours in the Japanese capital, but the hot and humid conditions from earlier in the week returned early on Wednesday with temperatures at times going above 30 degrees Celsius.

Vondrousova, who had shocked home favourite Naomi Osaka in the previous round, won the first set 6-3 at Ariake Tennis Park but her opponent was clearly struggling as she prepared to play the second set.

She required medical assistance to depart the court, as Vondrousova progressed to the final four.

VONDROUSOVA COMMENTS ON THE HEAT

The conditions for the tennis in Tokyo have been a quite literal hot topic with both Daniil Medvedev and Novak Djokovic stating matches should start at 3pm so the majority can be played as temperatures cool.

Vondrousova explained how it was playing in the searing heat, saying: "It was a big struggle from the beginning.

"I warmed up in the morning and I felt it was really hot and humid. Also, I was a bit tired from yesterday because I had doubles too.

"But I knew she had too [singles and doubles]. I felt like we both were struggling from the beginning.

"I was just thinking, you have to stay there mentally, just fight for every point and just see what happens. It's good for me that I can have some rest now.

"It's all about the head too. You have to stay there mentally and fight. Even when you lose the point, you have to get up and fight again. It's really a struggle here with the weather, but that's it, we have to fight."

OLYMPICS LIKE A SLAM FOR SVITOLINA

Next up for Vondrousova is a last-four meeting with Elina Svitolina, the fourth seed and highest-ranked player left in the women's draw.

The Ukrainian was a 6-4 6-4 victor over Camila Giorgi and talked up the significance of winning Olympic gold.

"I know that for Ukraine, [the Olympics] is a really big thing," Svitolina said. 

"I value the Olympics as a grand slam, and I tried to prepare to bring my best tennis. Here I am in the semi-final, and I can get a chance to get a medal. It's very special for me, but I try to take one match at a time."

Belinda Bencic (9) came through 6-0 3-6 6-3 against Anastasia Pavlyuchenkova on the other side of the draw. She will face Elena Rybakina (15), who was too good for seventh seed Garbine Muguruza in a 7-5 6-1 win.

Ash Barty was beaten along with partner Storm Sanders in the women's doubles quarter-finals earlier on Wednesday but the world number one bounced back to win her first-round mixed doubles match with partner John Peers.

The Australian duo beat Argentina's Horacio Zeballos and Nadia Podoroska 6-1 7-6 (7-3).

Daniil Medvedev told the chair umpire "I can finish the match but I can die" as he struggled with the suffocating heat at Tokyo 2020.

A 6-2 3-6 6-2 win over Fabio Fognini on Wednesday was enough to see Medvedev through to the last eight at Ariake Tennis Park.

But the world number two struggled with 72 per cent humidity that meant an already hot 31 degrees Celsius felt like 37 degrees Celsius on the heat index.

An extreme heat rule meant Medvedev and Fognini were allowed to leave the court for 10 minutes at one stage of the contest.

Medvedev was in visible discomfort before serving, between points and at changeovers. 

He had two medical timeouts before being asked by the chair umpire Carlos Ramos whether he could continue.

"I can finish the match but I can die," the Russian replied to Ramos, per ESPN. "If I die, are you going to be responsible?"

After the match, Medvedev – who along with Novak Djokovic has been vocally calling for matches to start later in the day to counteract the heat – described his struggles.

He said: "Even from the first set, I didn't feel good enough with my breathing. That's why I called the physio. I felt like my diaphragm had blocked. 

"I couldn't breathe properly. I think it was the most humid day we have had so far.

"Then, on the second set, I just had darkness in my eyes, like between every point I didn't know what to do to feel better. 

"I was bending over, and I couldn't get my breathing together. I was ready to just fall down on the court.  

"I knew there was a 10-minute break. So I went under the cold, freezing shower.

"When you have such a change of temperature and go out on the hot court, you can fully cramp, and it finishes the match for you, either that or you feel better. I was lucky I felt better.

"I don't care too much [about closing the roof], to be honest because I don't know if they have AC [air-conditioning]. 

"It can be actually more humid and hot when they close it, but they should start the matches later. I said it in the first round, and I'll continue saying it.

"All the players I know said this is not normal to start at 11am [local time]. 

"[Djokovic] went to ITF and talked to them, and they gave him reasons - I heard maybe from tomorrow they're going to change it, but let's see."

Following the Medvedev match, organisers were quoted as saying they were "considering" making a change, starting from Thursday's action.

Paula Badosa also struggled on Wednesday and ultimately had to leave the court in a wheelchair after retiring with heatstroke from her quarter-final match against Marketa Vondrousova. 

The Spaniard also withdrew from her mixed doubles match later alongside Pablo Carreno Busta, ending their hopes.

Carreno Busta is still in the singles and will face Medvedev next.

Vondrousova, who had won the first set before her opponent withdrew, said: "It was a big struggle from the beginning because I warmed up in the morning and I felt it was really hot and humid.

"Also, I was a bit tired from Monday because I had doubles too. But I knew [Badosa] had [played singles and doubles] too. 

"I felt like we both were struggling from the beginning. I was just thinking, you have to stay there mentally, just fight for every point and just see what happens."