Carlos Alcaraz was lost for words after making history in the Spanish teenager's shock five-set upset of world number three Stefanos Tsitsipas at the US Open.

Alcaraz – rated by many as Spain's best young male player since 20-time grand slam champion Rafael Nadal first emerged – sent Tsitsipas packing 6-3 4-6 7-6 (7-2) 0-6 7-6 (7-5) in the third round on Friday.

The 18-year-old Alcaraz became the youngest player to reach the last 16 of the US Open since Americans Michael Chang and Pete Sampras in 1989.

Alcaraz also became the youngest man to beat a top-three opponent at the tournament since the ATP introduced its world ranking system in 1973.

After more than four hours on Arthur Ashe Stadium, Alcaraz told reporters: "I have not words to explain how I feeling right now.

"I just don't know what happened out there in the court. I can't believe that I beat Stefanos Tsitsipas in an epic match.

"For me it's a dream come true."

Amid comparisons with countryman Nadal, Alcaraz added: "Honestly I don't copy any style of a players. I just play my game.

"But if I have to say one player that is similar my game, I think it's [Roger] Federer. I think similar as mine game, trying to be aggressive all the time. I think it's a good similar for me."

After his US Open campaign came to a surprise end, third seed Tsitsipas tipped Alcaraz for future success.

"A hundred percent," Tsitsipas replied when asked if he had a sense of Alcaraz's potential. "I said he can be a contender for Grand Slam titles. He has the game to be there."

"I've never seen someone hit the ball so hard," French Open runner-up Tsitsipas added. "Took time to adjust. Took time to kind of develop my game around his game style.

"It's one of these matches and one of these feelings where, you know, you pick up at some point of the match, you feel like you're in control, and it doesn't really go your way at the end.

"It's kind of bitter, I would say, especially after such an incredible first set by my side, dominating, being just so aggressive, not dwelling on the past. It was a great first set.

"I don't know. I felt like he played the fifth one completely -- the way he played the first set basically, careless, going for every single shot. I have never seen someone play such a good fifth set, honestly."

Naomi Osaka's quest for back-to-back US Open crowns came to a shock end, the defending champion imploding in a remarkable 5-7 7-6 (7-2) 6-4 loss to teenage sensation Leylah Fernandez.

Up a set and 6-5, Osaka had the chance to close out the third-round contest before the four-time major champion suffered an epic meltdown on Arthur Ashe Stadium, where fans booed the titleholder.

Osaka – typically reserved and quiet but in the spotlight amid her mental health concerns after withdrawing from the French Open, having skipped Wimbledon – threw her racquet three times in the unsuccessful second-set tie-break on Friday.

The Japanese star received a warning after hitting a ball into the crowd in the final set and while she tried to dig herself out of a hole, 18-year-old Canadian Fernandez completed a stunning upset in New York.

Fernandez showed no fear in her first career meeting with Osaka, going toe-to-toe against the former world number one.

There were no breaks of serve through nine games – Osaka serving to stay in the set at 5-4 and she did so easily before flicking the switch.

Osaka broke to love in the very next game, reeling off nine successive points to take the opening set.

In the third round of the US Open for the first time and with a 1-2 record against top-10 players, Fernandez was not overawed on the big stage.

Behind her big first serve and powerful baseline hitting, Fernandez ensured the second set followed a similar pattern as Osaka was prevented from racing away with the match.

It appeared as though the second set would go down the same path as the first after Osaka broke for a 6-5 lead.

But Osaka imploded on centre court – after failing to serve out the match, she lost her composure in the tie-break, throwing her racquet on numerous occasions as Fernandez forced a deciding set with ease.

Osaka immediately left the court and emerged with a towel over her head before the start of the final set, however, she still looked off her game, broken in the opener.

Continuing to struggle, Osaka was then given a warning for hitting the ball into the crowd, though she boosted her confidence by holding serve and avoiding falling 3-0 behind.

But Fernandez's sole break point was all she needed, sending the defending champion home, much to the delight of the crowd.

Data slam: Fernandez steps up

Her only top-10 victory came against Belinda Benic at the 2020 Billie Jean Cup, having lost to Elina Svitolina and Sofia Kenin last year. But Fernandez claimed the unlikely scalp of Osaka on Friday. The result also ended Osaka's bid to come the first woman to defending the US Open since Serena Williams in 2014.

WINNERS/UNFORCED ERRORS

Fernandez – 28/24
Osaka – 37/35

ACES/DOUBLE FAULTS

Fernandez – 6/2
Osaka – 15/2

BREAK POINTS WON

Fernandez – 2/5
Osaka – 2/5

Carlos Alcaraz put his name up in lights in New York as the 18-year-old stunned third seed Stefanos Tsitsipas in a massive US Open third-round upset.

Spanish teenager Alcaraz scored an astounding 6-3 4-6 7-6 (7-2) 0-6 7-6 (7-5) victory in a battle lasting four hours, seven minutes inside Arthur Ashe Stadium on Friday.

French Open runner-up Tsitsipas became the biggest casualty of the men's tournament so far as hot prospect Alcaraz showed his mettle on the grand slam stage at Flushing Meadows.

It means Alcaraz, rated by many as Spain's best young male player since Rafael Nadal first emerged, has reached the fourth round of a major for the first time in his career.

He becomes the youngest player to reach the last 16 of the US Open since Americans Michael Chang and Pete Sampras in 1989.

The US Open said the win made Alcaraz the youngest man to beat a top-three opponent at the tournament since the ATP introduced its world ranking system in 1973.

Alcaraz put a dire fourth set behind him and looked to have won the match with a lob at 6-4 in the deciding tie-break, but his ball landed a whisker long.

That meant the players were back on serve, but Alcaraz was unbowed and sealed victory with a scorching forehand winner, announcing himself as a likely superstar of the near future. He struck 61 winners in all.

He will face German qualifier Peter Gojowczyk in the fourth round, with a quarter-final place at stake.

Speaking on court after his win, Alcaraz hailed the supportive New York spectators who were firmly in his corner.

"I think without this crowd I haven't the possibility to win this match," he said. "Thank you to you the crowd for pushing me up in the fifth set

"It has been an incredible feeling for me. This victory means a lot to me. It's the best match of my career, the best win.

"For me to beat Stefanos Tsitsipas is a dream come true for me and to do it here is more special."

Novak Djokovic says he was not acting like a "spoiled brat" when he complained about a rowdy spectator during his US Open defeat of Tallon Griekspoor.

World number one Djokovic took another stride towards a first calendar Grand Slam and a record 21st major title by beating Dutchman Griekspoor 6-2 6-3 6-2 in the second round on Thursday.

Top seed Djokovic, who will face Kei Nishikori in the third round, had to contend with a member of the crowd trying to unsettle him in Arthur Ashe Stadium.

He shouted as the Serb went for an overhead smash that he missed and continued to be vocal during points, prompting Djokovic to express his grievances with the chair umpire.

Djokovic feels it is important to make it clear that sort of behaviour should not be tolerated.

"When tennis players talk about that, someone who is watching team sports would say, 'What a spoiled brat'," the three-time US Open champion said.

"But it's a different sport. Look, there's a lot of noise happening on the stadium, particularly in the night sessions. I don't mind that.

"Even sometimes during the point it happens that people out of excitement, they just scream, or they release like a sound or whatever, sigh, whatever you call it. And that's fine.

"But if someone intentionally does it over and over again, then I have tolerance up to a certain point, then it's not correct, then it's not fine. It's not fair. I feel like it's not good for us players.

"I mean, particularly that guy for some reason was calling, raising the sound and kind of screaming just before I would hit my smash, which was a big point. Before that he would do [it] a few times. After that again.

"That wasn't nice. That's all. I don't mind the noise. Don't get me wrong. I think it's important for the entertainment, for the crowds, the music.

"I get it. But if someone does it over and over again, particularly when you are at his side, he knows why he's doing it. The guy that I pointed out, he knew exactly what he was doing, and that's all."

Novak Djokovic welcomed the ongoing 'GOAT' discussion alongside Rafael Nadal and Roger Federer after the world number one took another step towards an historic grand slam title at the US Open.

Djokovic, Nadal and Federer share the most men's slams in history with 20 but the former has the chance to break the record at Flushing Meadows, where the top seed dismantled unheralded Dutchman Tallon Griekspoor 6-2 6-3 6-2 in the second round on Thursday.

Serb star Djokovic is also bidding to become just the third man to complete a calendar Grand Slam and the first to sweep all four majors in a year since Rod Laver in 1969.

It is widely debated who is the greatest player of all time among Djokovic, Nadal and Federer – the latter two are both absent from this year's US Open due to injury.

After reaching the third round in New York, Djokovic was asked who the better player on a neutral surface is, given Nadal's clay-court dominance and Federer's grass-court expertise.

"It's difficult to say who is better. Three of us, we're all so different. We have different styles," Djokovic said during his post-match news conference.

"We have different trajectories or journeys to where we are at this moment. We all had tremendous success, some more particularly on one surface, some the other surface.

"We do complement each other. I think the rivalry between the big three, so to say, it's phenomenal for our sport.

"So the more traction, the more conversation there is around the three of us, the GOAT discussion, et cetera, the better in general for our sport. I hope people still keep on talking about it."

Djokovic added: "I think actually one of the best I think images that I've ever seen from tennis is them [Nadal and Federer] playing on a half-grass, half-clay court.

"I thought that was fantastic. Whoever came up with the idea was genius. As a tennis fan, I enjoyed that very much."

Djokovic hit 33 winners, fired down 13 aces and broke six times throughout a dominant performance against Griekspoor under the Arthur Ashe Stadium lights.

The 34-year-old also improved to 53-1 against non-top 100 opponents at majors, while he is now 13-0 against them at the US Open.

Kei Nishikori awaits Djokovic, who owns a 17-2 head-to-head record against the 2014 US Open runner-up.

"We played many times. I have very good score against him," Djokovic said of Nishikori. "I lost I think last time here in New York in semis in 2014. Historically I think his most successful grand slam is here. He's one of the quickest and most-talented players that I've seen in my lifetime, in my career.

"I think it's important for me to serve well and try to take off the pace a little bit because he likes the pace. He likes to hit the ball early, protect the line. But I know his game well. We played in Olympic Games. I know what's expecting me. I look forward to a good challenge."

History-chasing world number one Novak Djokovic cruised through to the third round of the US Open at the expense of Tallon Griekspoor 6-2 6-3 6-2.

Djokovic is bidding to become just the third man to complete a calendar Grand Slam and the first to sweep all four majors in a year since Rod Laver in 1969.

The top seed, who is also pursuing a record-breaking 21st slam crown – currently level with injured stars Rafael Nadal and Roger Federer on 20 – outclassed Griekspoor in one hour, 39 minutes on Thursday.

Awaiting Djokovic is 2014 US Open finalist and Japanese star Kei Nishikori in the third round.

Djokovic, who withstood a spirited challenge from Holger Rune in the opening round before the teenager succumbed to cramps, asserted his dominance against Griekspoor from the outset on Arthur Ashe Stadium.

Boasting a 14-0 record in second-round matches at the US Open, Djokovic only lost one point on his first serve in the opening set and fired down five aces, while hitting 13 winners and converting two of his three break points.

While world number 121 Griekspoor managed to break Djokovic's serve in the second set, the Serb was typically efficient as he builds towards another shot at history in New York.

Coming to the net more in the third set, Djokovic was determined to get off the court as quickly as possible and he did just that – saving three break points en route to another third-round appearance at the year's final slam.

Data slam: Djokovic continues strong record

The 34-year-old came into the contest with a 52-1 slam record against non-top 100 opponents. Djokovic improved to 53-1 – his lone loss to world number 117 Denis Istomin at the 2017 Australian Open – and a perfect 13-0 at the US Open with his straight-sets victory.

WINNERS/UNFORCED ERRORS

Djokovic – 33/20
Griekspoor – 20/28

ACES/DOUBLE FAULTS

Djokovic – 13/5 
Griekspoor – 5/2

BREAK POINTS WON

Djokovic – 6/10
Griekspoor – 1/4

World number one Ash Barty said her serving struggles are "not a concern" after advancing to the US Open third round.

Barty continued her quest for a third grand slam title and first US Open crown with a 6-1 7-5 win over teenage prodigy Clara Tauson on Thursday.

Reigning Wimbledon champion Barty hit 33 winners and fired down 11 aces to see off the 18-year-old on Arthur Ashe Stadium in New York.

Barty, though, had to stave off a late challenge just like the top seed did against Vera Zvonareva in the opening round.

After she faltered to serve out the match at 5-4 in the second set of her victory over Tauson, Barty said: "It's happened a few times, but I have won 40-odd matches [this year] and it hasn’t happened a lot.

"It's just a few of those games I haven't been able to get up and hit my spots on first serves.

"When you give good players looks at second serves, you're going to get hurt. It's simple as that. It’s not a concern."

Barty leads the WTA Tour this season for titles won (five), match victories (42), finals reached (six), aces (319) and top-10 wins (seven).

"There's room for improvement, without a doubt, but there's room for improvement every single day," said Barty, who has never reached the quarter-finals at Flushing Meadows.

"Credit to her, she was a little bit more aggressive in that second set. I got a little bit passive and just let my energy drop and allowed her back in.

"We'll go back and have a chat about the matches and, once we get back on the practice court, try and fix a few things up, trust myself and trying to continue to play how I want to play."

Next up for Australian star Barty is either 2020 US Open quarter-finalist Shelby Rogers or Sorana Cirstea.

Alexander Zverev believes his comeback victory over Novak Djokovic at the Olympics has paved the way for his fine start at the US Open.

Zverev came from a set down to defeat world number one Djokovic 1-6 6-3 6-1 at the semi-final stage in Tokyo, with the German going on to claim gold by beating Karen Khachanov in straight sets.

The world number four carried the winning form to Cincinnati, triumphing at the Western and Southern Open, and has made a smooth start at Flushing Meadows, where he lost out to Dominic Thiem in last year's final.

Zverev did not offer up a single break point in a dominant first-round win over Sam Querrey, and lost only four games when cruising past Albert Ramos-Vinolas 6-1 6-0 6-3 on Thursday.

"The process started at the Olympics for me, and the match against Novak," Zverev told reporters.

"That kind of started it off, because I was down badly, and I managed to win with great tennis.

"It was very important for me to kind of back it up in Cincinnati, because a lot of the times players that for the first time in their career win something really big like a grand slam title or a gold medal, they do tend to go downhill a little bit.

"So it was important for me to go to Cincinnati, to a place where I have never won a match before this year, and have a great tournament."

Another motivation for Zverev is the cruel fashion in which he lost to Thiem last year, when he surrendered a two-set lead.

"I mean I was the first man in 785 years to lose a US Open from two sets to love up and being a break up in the third set, serving for it in the fifth set, being two points away multiple times, it was painful," Zverev said with a smile.

"I still remember it, I remember it every single time I walk on this board but I take it as motivation because I'm back here to hopefully play a great tournament and win a grand slam title, that's what I’m here to do."

Zverev has now tallied up 40 wins in 2021 and 13 on the bounce, though the 24-year-old - who could meet Djokovic in the semi-finals - knows he has to maintain his strong service game to keep his best tennis.

"My serve is kind of the key to my game. When it's working I'm playing great. When it's not, I'm losing matches like I did at Wimbledon," he said.

"It's no secret that my serve is probably the most important shot in my game, and I'm happy with how it's working. The matches are not going to get easier and I will need that to be my weapon.

"I think it was always a problem of mine at the beginning of my career that I always spent a lot of hours, a lot of time in the beginning of grand slam tournaments. So it's nice to have two matches, winning [them] in straight sets."

The US Open was mounting a clean-up and safety check operation on Thursday after being affected by a deadly storm that struck New York City. 

There would be no play before 12:00 local time (16:00 GMT), an hour later than matches usually get under way, and spectators were told they would not be allowed into the grounds until 11:00 at the earliest. 

Severe weather hit New York and New Jersey on Wednesday, with the tail-end of Hurricane Ida striking the area and causing at least nine deaths. 

Eight of those deaths recorded in New York resulted from basements flooding, the New York Post reported, with the flash flooding causing chaos in large parts of the city. At one point, 3.15 inches of rain fell in an hour, a record for the Big Apple. 

Tournament organisers were carrying out inspections to determine whether safety of visitors to the Flushing Meadows grounds could be assured. 

The US Open said in a statement: "We appreciate your patience as we evaluate the readiness of our site. The safety of our fans, players and staff is of the utmost importance. 

"We will be issuing an update to the schedule including gate opening and match start times. The current plan will not open gates before 11:00 am." 

The storms were so unusually powerful on Wednesday that the late-night match between Kevin Anderson and Diego Schwartzman on the covered Louis Armstrong Stadium was affected by rain, with water gusting in through openings despite the protection. 

It was moved to Arthur Ashe Stadium to be completed, with its original court left drenched. 

Transport in New York early on Thursday was proving problematic, with the Metropolitan Transportation Authority, responsible for the local bus and subway system, announcing an "extremely limited" service and urging customers to "stay home if you can". 

Ash Barty and Novak Djokovic, along with Olympic champions Alexander Zverev and Belinda Bencic, are among those due in action on Thursday. 

Men's tennis would be a safe environment for any gay player ready to announce their sexuality, three of the brightest young talents in the game have said.

Speaking on the US Open's first Pride Day, Stefanos Tsitsipas, Daniil Medvedev and Felix Auger-Aliassime said players should not fear coming out.

A number of the best-known women's players of all time have been lesbian, including Martina Navratilova, Billie Jean King and Amelie Mauresmo.

However, there have been few modern-era 'out' gay stars on the men's ATP Tour, with Navratilova having said in the past that those that exist have been "so far in the closet I don't know who they are".

Russian world number two Medvedev said: "From my side, I think everybody would be super open if somebody would come out on the ATP Tour.

"The other question is: are there any gays on the ATP Tour? Again, until somebody comes out, you cannot know unless you're his best friend and you know what he goes through.

"I think it's great from the US Open, this initiative. I think the ATP honestly is doing a good job, also especially internally trying to provide info and to just make sure that if anybody wants to come out, he's gonna feel safe and secure.

"All the players would be happy for the guy if he does it."

Canadian rising star Auger-Aliassime, who like Medvedev and Tsitsipas has reached round three at Flushing Meadows, explained it was important for the tour to let players be themselves.

On the women's tour, Belgian players Alison van Uytvanck and Greet Minnen are engaged, while there are a number of other players from the LGBTQ (lesbian, gay, bisexual, transgender, queer/questioning) community.

But the men's tour in recent years has seen no such prominently out players, which world number 15 Auger-Aliassime finds surprising, given the high number of professionals.

"Recently I've started doing a survey inside the ATP about the LGBTQ+ community," Auger-Aliassime said.

"It's important these days to be aware of that and to be open-minded and the ATP needs to do that, in today's time it's needed.

"The reason we don't have openly gay players on the ATP Tour, I'm not sure of the reason, but I feel me, as a player, it would be very open, very welcome. Statistically there should be some, but for now there's not."

Tsitsipas was asked whether the tour would be a "safe space" now, for any player considering coming out.

"I think so. They would be supported, for sure," said the Greek world number three, speaking on Wednesday's Pride Day in New York.

"I don't know how it is in other sports. I see no reason, for example, a tour like the ATP not to accept something like this."

Sloane Stephens sent Coco Gauff spinning out of the US Open – then joined the clamour to stop toilet break "gamesmanship" in tennis.

In Wednesday's opening night match on Arthur Ashe Stadium, former champion Stephens took the fast route past world number 23 Gauff, speeding to a 6-4 6-2 victory.

Now ranked 66th, Stephens won at Flushing Meadows in 2017 and was tipped by Gauff to challenge for the title again this year. By beating Madison Keys and now Gauff, Stephens is showing she still has major game, and another former champion in Angelique Kerber could be her third-round opponent.

Gauff, now 17, has known Stephens for over seven years, having attended the now 28-year-old's 21st birthday party.

But the American pair put friendship to one side for their showdown, with Gauff, who had been fancied by many to go deep this fortnight, having her threat stifled by an in-form Stephens.

"I think the last time we hit, she was probably like 12. It was a little bit different," Stephens said afterwards.

"It's just been really nice to see her game kind of evolve and the things that she's doing, like how she's able to turn so much defense into offense and kind of do those movements. She is great at the net. She has a really great all-around game. It's been really nice to see.

"She's different from a lot of the up-and-coming players we're seeing now that are just super hard hitting, not much variety. She has a lot of variety. I think a lot of the younger girls, there's half that are very hard hitting and half that have a lot of variety. I think she's in the bucket with a lot of variety."

Gauff was asked whether Stephens could now be considered a title contender and replied: "Yeah, definitely. Today she was playing well. I knew these last couple of tournaments she's been playing better and better. I hope that she can make it all the way to the end.

"Obviously if you are going to lose, you want to lose to the champion. I think that I feel like I've learned that I'm capable of making it far in slams. I think if I tighten up a few things, that I'm capable of winning one."

The debate over toilet breaks in tennis was sparked by Andy Murray being furious with Stefanos Tsitsipas for spending eight minutes in the bathroom before tackling the Scot in the deciding set of their first-round match.

Murray, frustrated to be left waiting for his opponent to reappear, followed up his Monday night fury with a tweet that charged Tsitsipas with taking twice as long to visit the toilet as Amazon mogul Jeff Bezos took to travel into space.

There was no such spat in Stephens' quickfire win over Gauff, but the rules on spending a penny have been the currency of many a news conference this week.

"I honestly just thought Andy's tweet was really funny," said Stephens. "I didn't see exactly what happened. I'm not sure. I just thought it was hilarious. We all are like huge Andy fans. We love him.

"I can't speak for what happened in that match, but I do know on the girl's side, there still is a lot of that. It's gamesmanship.

"I think there definitely needs to be a rule or changes. They make a lot of rule changes for smaller things, like they took one minute off the warm-up. If someone goes to the bathroom for nine minutes, no one says anything.

"Six, eight minutes is a long time to leave a match. That changes the whole momentum of a match. If you're changing your clothes, what are you changing? What are you doing in there?

"When you get into six, seven, eight, nine minutes, okay, what are you doing in there? Do you need help? I can come help you. Like, what's happening? I think that's more where the issues are because it just becomes pure gamesmanship."

Two-time major winner Victoria Azarenka says it is "bizarre" that fans need to be vaccinated to attend the US Open but not the players.

The 2021 US Open marks the first tennis tournament where fans must show their proof of COVID-19 vaccination in order to attend matches inside the Flushing Meadows venue. The decision was made less than 72 hours prior to the first matches at the US Open.

Azarenka, who defeated Italian Jasmine Paolini 6-3 7-6 (7-1) in the second round on Wednesday, said there was a double standard applied for fans compared to players who are not required to be vaccinated to play.

"I want to start this conversation between our players, because to me that's a bit bizarre that fans have to be vaccinated and players are not," three-time US Open finalist Azarenka told reporters.

"I think it's inevitable that it will be mandated at some point, like other leagues are doing.

"I don't see the point of stalling it, because I think we all want to be safe, we all want to continue doing our jobs, and I know there is a lot of discussions about it."

She added: "I hope that as an association we make the best decision for our business, for our health, for the tournaments and for the public."

On Saturday, Briton Andy Murray voiced his opinion that players need to be vaccinated, saying it is their responsibility as they travel the world to play.

Numerous top players including Novak Djokovic, Stefano Tsitsipas and Daniil Medvedev have previously spoken about their concerns about getting vaccinated.

Medvedev would not be drawn on Azarenka's comments after he defeated Dominik Koepfer 6-4 6-1 6-2 in the second round on Wednesday.

"Tough to answer this question," Medvedev told reporters. "I think everybody can have his own opinion.

"I understand why they did it to the fans. So far it has not been applied to the players. We as players, we can just follow the guidelines and the rules. That's all we can do.

"I think it's not for players to decide, because that's why we have governing bodies in tennis."

Stefanos Tsitsipas has defended his "personal need" for long bathroom breaks after being jeered during his four-set second round win over Adrian Mannarino at the US Open on Wednesday.

The world number three triumphed 6-3 6-4 6-7 (4-7) 6-0 but was booed by the Arthur Ashe Stadium crowd after taking a bathroom break which exceeded seven minutes.

The Greek was criticized by Andy Murray, who said he lost respect for Tsitsipas after taking a lengthy break ahead of the final set in their five-set first round epic on Monday.

Alexander Zverev weighed in on the discussion, claiming Tsitsipas was communicating with his coach during his bathroom breaks, labelling them "ridiculous" and saying he had broken an "unwritten law".

Tsitsipas reverted to the rule book in his defence after beating Mannarino, insisting he had done nothing illegal and longer breaks were part of his "personal needs".

"It's just my personal needs," Tsitsipas told reporters. "Some people have other needs. Some people take much more than 25 seconds between points, which is fair.  

"I've done everything the right way. If I haven't I should be penalized. I completely agree with it. I should get a fine or be penalized if I haven’t followed whatever I've done correctly. But as far as I know, it is a necessity, it is a need when I'm out there playing and performing."

Tsitsipas said he felt fans who booed and jeered did not understand the game or his need to take longer bathroom breaks.

"I haven’t done anything wrong so I don't understand," he said. "The people love the sport, they come to watch tennis. I have nothing against them. But some people don't understand. They haven't played tennis at high level to understand how much effort and how much difficult it is to do what we are doing."

He added: "It is important. First of all, you carry less weight on you with all the sweat. You feel rejuvenated, you feel fresh, and you don't have all the sweat bothering you and coming in your face, on your fingers, everywhere all over your body. It makes you feel better.

"For me it is important to take that break. For someone else probably not. And everyone has his own time. I try and be as quick as I can. Sometimes I just need a bit more time."

Tsitsipas added that he was taken aback by the public criticism from Murray and Zverev.

"I never complain of what other players do," the 23-year-old French Open runner-up said. "My parents have taught me not to watch other people's business and concentrate on myself. Do my job.

"I just don’t understand when some players go and criticize other players, or during a match they put too much emphasis on it."

There have been calls for a hard cap on the permitted time for bathroom breaks, which American Sloane Stephens agreed with, speaking after her straight-sets win over 21st seed Coco Cauff.

"I don't think you should be gone from the court for six-eight minutes," Stephens said. "It's a long time to leave a match. That changes the whole momentum of a match.

"I can't speak for what happened in that match, but I do know on the girls' side, there still is a lot of that. It's gamesmanship.

"I think there definitely needs to be a rule or changes. They make a lot of rule changes for smaller things, like they took one minute off the warmup. If someone goes to the bathroom for nine minutes, no one says anything."

Two-time major winner Victoria Azarenka says it is "bizarre" that fans need to be vaccinated to attend the US Open but not the players.

The 2021 US Open marks the first tennis tournament where fans must show their proof of COVID-19 vaccination in order to attend matches inside the Flushing Meadows venue. The decision was made less than 72 hours prior to the first matches at the US Open.

Azarenka, who defeated Italian Jasmine Paolini 6-3 7-6 (7-1) in the second round on Wednesday, said there was a double standard applied for fans compared to players who are not required to be vaccinated to play.

"I want to start this conversation between our players, because to me that's a bit bizarre that fans have to be vaccinated and players are not," three-time US Open finalist Azarenka told reporters.

"I think it's inevitable that it will be mandated at some point, like other leagues are doing.

"I don't see the point of stalling it, because I think we all want to be safe, we all want to continue doing our jobs, and I know there is a lot of discussions about it."

She added: "I hope that as an association we make the best decision for our business, for our health, for the tournaments and for the public."

On Saturday, Briton Andy Murray voiced his opinion that players need to be vaccinated, saying it is their responsibility as they travel the world to play.

Numerous top players including Novak Djokovic, Stefano Tsitsipas and Daniil Medvedev have previously spoken about their concerns about getting vaccinated.

Medvedev would not be drawn on Azarenka's comments after he defeated Dominik Koepfer 6-4 6-1 6-2 in the second round on Wednesday.

"Tough to answer this question," Medvedev told reporters. "I think everybody can have his own opinion.

"I understand why they did it to the fans. So far it has not been applied to the players. We as players, we can just follow the guidelines and the rules. That's all we can do.

"I think it's not for players to decide, because that's why we have governing bodies in tennis."