Novak Djokovic has history in his sights as he begins his US Open quest; after three grand slam titles in 2021, a fourth beckons at Flushing Meadows.

Rod Laver was the last man to achieve a sweep of the Australian Open, French Open, Wimbledon and US Open singles in the same year, all the way back in 1969.

Steffi Graf won all four on the women's side in 1988, and it seemed a knock-in that Serena Williams would do likewise in 2015 when she headed to the US Open with three majors already bagged.

But winning any title at that level is never easy, and Williams famously came unstuck when she faced Roberta Vinci in the semi-finals.

Djokovic will be mindful that what seems an inevitability to the outside world remains very much still only a possibility. After his US Open tribulations last year, and a recent jolt at the Olympics, he will know anything can happen.

Here, Stats Perform looks at how Djokovic's situation at Flushing Meadows carries most of the hallmarks of Serena's own position as she headed into the tournament six years ago.

IT'S ALL ABOUT THE SLAMS

It was not always this way, but Djokovic has reached the point in his career when he can choose targets, decide which records he wants to break, and throw everything at those goals.

At the start of the year in Australia, he savoured triumphing at Melbourne Park for a ninth time and pointed to how Roger Federer, Rafael Nadal, Williams and Margaret Court had achieved so much.

"They've made history already," Djokovic said. "They made a tremendous mark in our sport. I'm trying to build that and develop that myself in a very unique, authentic way that is suitable to me.

"Whether I think about winning more slams and breaking records, of course. Of course, I do. And most of my attention and my energy from this day forward, until I retire from tennis, is going to be directed in majors, trying to win more major trophies."

It had very clear echoes of Williams in 2015, also in Australia, setting out her own ambitions for the year and specifically targeting the French Open and Wimbledon.

"Those are the two I really have my eye on, because I would like to do better at those. And I know I can do better," she said.

Williams set her heart and mind on that twin challenge and won both.

"I definitely am not going to play as much this year, and I'm just going to go for everything when I do play," said Williams.

BUILDING UP

When Williams reached New York in August 2015, she had delivered a 48-2 win-loss record for the season, landing each of the majors alongside the Miami Open and the Western and Southern Open. Petra Kvitova in Madrid and Belinda Bencic in Toronto had been the only two players to get the better of the 33-year-old Williams.

Djokovic has a 38-5 record for the year, albeit it has the feel of a more dominant year for the 34-year-old Serbian. Two of those losses came at the Olympics, in a semi-final and bronze medal match, and the other three came in his first three events on clay, losing to Dan Evans in Monte Carlo, Aslan Karatsev in Belgrade and Nadal in Rome.

When it mattered on clay, though, Djokovic majorly turned up in Paris, gutsily beating Lorenzo Musetti from two sets down in the fourth round, ending Nadal's streak of four Roland Garros titles by sinking the Spaniard in the semi-finals, and then leaving Stefanos Tsitsipas devastated in the final, with another fightback after dropping the first two sets.

Wimbledon followed, and Djokovic by then was openly targeting a Golden Slam – each major and the Olympic title.

Much like with Williams and her loss to Bencic in the Toronto semi-finals six years ago, however, Djokovic showed he was fallible as history beckoned. From a set up, he lost to Alexander Zverev at Tokyo 2020, a blow that was compounded by missing out on bronze when Pablo Carreno Busta sprang another shock.

HISTORY CAN BE A FIERCE OPPONENT

Williams and Djokovic have won non-calendar Grand Slams before, winning four in succession spanning two seasons.

Williams first achieved that from the French Open in 2002 to the Australian Open in 2003, and in 2015 she was aiming for five slams in a row at the US Open, having begun her dominant streak at her home grand slam the previous year.

She won the first set of the semi-final against Vinci, the world number 43, but was then second best to the Italian, with Williams saying her conqueror "played literally out of her mind".

But the disappointment was stark, underlined by Williams' terse response to the question of how disappointed she felt by the result.

"I don't want to talk about how disappointing it is for me," she said. "If you have any other questions, I'm open for that."

The four-in-a-row feat has only been performed once by Djokovic, from Wimbledon in 2015 to the French Open in 2016. Had he not been disqualified during the US Open last year for carelessly hitting a ball that struck a line judge, he would most likely currently be on a four-slam streak.

Those who win the first three slams of the year often do complete the set, but there are four instances of singles players falling one short by failing in the year's last major.

Before Williams, the most recent case was Martina Navratilova in 1984, when the imperious left-hander headed to the Australian Open – then played at the end of the year rather than the start – in pursuit of the Grand Slam. She lost to Helena Sukova in the semi-finals, and said: "If I'd have won, I'd have done it all. If I lost I had to start from scratch. Both are hard to cope with."

Navratilova had won 74 consecutive matches until that loss and ended the season with a 78-2 record.

In the men's game, Jack Crawford (1933) and Lew Hoad (1956) also fell short, both losing in finals of the US National Championships, the tournament that became the US Open. Don Budge (1938) and Laver (1962 and 1969) are the only men to have won a calendar Grand Slam in singles.

The weight of expectation is immense for Djokovic as he pursues what would be his crowning glory, not only sealing the Grand Slam but reaching 21 majors, one ahead of Nadal and Federer and into the outright lead in the men's game. The prospect cannot be ignored, and it will be a heavy burden to carry over the coming fortnight.

As Djokovic said on Friday: "I would be lying if I said that’s not something that I’m thinking about or that my attention is not going that way.

"I’m very motivated to play my best tennis. But I have to hit one ball at a time, as they say, try to be in the moment, have a guiding star in a way, a dream to win a slam here."

Elina Svitolina claimed her first title of the year with a hard-fought victory over Alize Cornet at the Chicago Women's Open.

Svitolina won in straight sets in tough conditions, though she needed two hours and two minutes to record a 7-5 6-4 triumph over her French opponent.

Cornet had won their previous meeting at Eastbourne in 2019 but the world number 68 was unable to pull off a repeat result against the tournament’s top seed in Illinois.

A see-saw contest saw 10 breaks of serve, starting with the second game as Svitolina struck an early blow while racing into a 3-0 lead.

However, Cornet clawed her way back to get on level terms and a tie-break looked likely until she was broken in a lengthy 12th game.

The second set followed a similar pattern as Svitolina again won the opening three games. After a medical timeout, Cornet cut the deficit to 3-2 but was not able to get back on level terms, the pair exchanging six breaks through to the conclusion.

Having failed to serve out for the victory, Svitolina finally secured a first tournament triumph since Strasbourg in 2020 thanks to a superb backhand.

It is her 16th title overall and comes as ideal preparation ahead of the US Open, where the Ukrainian will face qualifier Rebecca Marino in the opening round in New York.

Anett Kontaveit ended a four-year title drought by beating Irina-Camelia Begu to win the inaugural Tennis in the Land event on Saturday.

Kontaveit had failed to win a tournament since her maiden WTA Tour triumph in 's-Hertogenbosch back in 2017 before defeating Begu 7-6 (7-5) 6-4.

The world number 30 from Estonia had lost two finals this year, but she was not to be denied in Cleveland.

Begu fought back from 5-2 down in the first set to force a tie-break, but one mini-break was enough for second seed Kontaveit to take a big stride towards an elusive title.

The composed Kontaveit did not face a break point in a tight second set, not allowing her Romanian opponent a look-in as she served superbly.

Kontaveit only had one break-point opportunity of her own, but grasped it to lead 2-1 and went on to seal a confidence-boosting triumph ahead of the US Open.

Sam Stosur will be Kontaveit's opponent in the first round at Flushing Meadows, while Begu faces Andrea Petkovic.

Defending US Open champion Naomi Osaka believes she could have better handled her decision not to participate in media conferences at the French Open.

Osaka withdrew from the French Open having won her first-round match, after she was fined and threatened with further punishment – and possible expulsion from the grand slam – for skipping obligatory media duties.

The four-time grand slam champion had confirmed before Roland Garros that she would not be taking part in post-match news conferences, suggesting her mental health was not helped by having to attend the mandatory interviews.

Osaka, the world number three, stated she has had "long bouts of depression" since winning the 2018 US Open title.

The 23-year-old subsequently pulled out of Wimbledon, but returned as one of Japan's great hopes for the Tokyo Olympics.

However, she suffered a surprise defeat to Marketa Vondrousova, while her preparation for Flushing Meadows also took a hit with a last-16 loss to Jil Teichmann in Cincinnati earlier this month.

Reflecting on her decision in Paris, Osaka, who won her second US Open title in 2020, told reporters: "I feel there's a lot of things that I did wrong in that moment.

"But I'm also the type of person that's very in the moment.

"I think there's a lot of things that I learned to do better. Of course, I don't feel the same situation will happen again.

"Whatever I feel, I'll say it or do it. I don't necessarily think that's a bad thing.

"I would say, maybe think it through a bit more, in the way that I didn't know how big of a deal it would become."

A few days prior to her defeat to Teichmann, Osaka broke down in tears during her first news conference since she pulled out of Roland Garros.

Yet the Queens-raised star was more composed during her media duties on Friday, as she aims to cap off what has been a difficult 2021.

"I think the biggest memory that comes back to me is being a little kid, running around the entire site," said Osaka, who will take on Marie Bouzkova to get her title defence started.

"I don't know if that may be the reason why I play so well here, but there's definitely a lot of nostalgia.

"I know I haven't played that many matches. But actually I feel pretty happy with how I'm playing."

Elina Svitolina is in position to win her first title of 2021 after outlasting Rebecca Peterson to reach the Chicago Women's Open final. 

After dropping just one game in her quarter-final win over Kristina Mladenovic, Svitolina needed nearly two and a half hours to dispatch Peterson 6-1 6-7 (4-7) 6-3 on Friday.

The top seed will seek her 16th career WTA Tour title against ninth-seeded Alize Cornet, who rallied to defeat Varvara Gracheva 4-6 6-1 6-0 in the other semi. 

Gracheva's capitulation after winning the first set was understandable, as earlier in the day she had finished off a quarter-final upset of eighth seed Marta Kostyuk in a match that had been suspended due to darkness Thursday. 

Gracheva prevailed 6-7 (4-7) 6-3 6-4 in that contest, with play on Friday beginning late in the second set, but did not have enough to pull out another win. 

The final will feature the eighth head-to-head meeting between Svitolina and Cornet, with the Ukrainian holding a 4-3 edge. 

At Tennis in the Land, second seed Anett Kontaveit defeated seventh seed Sara Sorribes Tormo 6-4 6-4 in one semi-final. 

She will meet Irina-Camelia Begu in the final of the Cleveland tournament after the unseeded Romanian upset sixth seed Magda Linette 7-6 (7-5) 6-2. 

Kontaveit won her first WTA title at Guadalajara earlier this year, while Begu will be seeking her fifth Tour title and first since 2017.

Australian Open chief Craig Tiley is confident the season-opening grand slam will be held in Melbourne next year, despite coronavirus concerns.

COVID-19 continues to wreak havoc around much of Australia, with Victoria and New South Wales both locked down due to outbreaks in the states.

The 2021 Australian Open went ahead, albeit in February instead of January, amid the coronavirus pandemic and without fans for most of the tournament following a snap lockdown of Melbourne.

Novak Djokovic was among the players critical of the conditions athletes endured prior to this year's Australian Open, with strict quarantine measures introduced.

Players, however, as set to spend two weeks in a biosecure bubble prior to the 2022 event, according to Tiley.

"There's a lot of time between now and when we get going but, at this point in time, we're planning on having a two-week bubble, where the players will be able to move freely between the hotel and the courts," Tiley said.

"They're protected, they're kept safe among themselves and safe from the community as well.

"And after those two weeks, they'll come out and be able to compete in the Australian Open in front of crowds."

Stefanos Tsitsipas faces Andy Murray and Ash Barty will take on 2010 finalist Vera Zvonareva in the first round of the US Open.

French Open runner-up Tsitsipas and 2012 champion Murray is one of the standout matches in the opening round at Flushing Meadows.

Top seed Novak Djokovic will start his quest for a calendar Grand Slam against a qualifier in New York and could face a repeat of the Wimbledon final versus Matteo Berrettini in the last eight.

World number one Djokovic, a strong favourite for a record 21st major title with Rafael Nadal and Roger Federer absent due to injury, could do battle with Alexander Zverev at the semi-final stage.

Daniil Medvedev, the second seed, is in the bottom half with Tsitsipas, who he could come up against in the semi-final. Medvedev's first test will come against Frenchman Richard Gasquet.

Barty could come up against Iga Swiatek in the last eight and Karolina Pliskova if she makes it through to the semi-finals.

Simona Halep's encounter with Camila Giorgi is a mouthwatering first-round match, while defending champion Naomi Osaka returns to grand slam action against former US Open junior champion Marie Bouzkova.

Angelique Kerber could be a tough fourth round opponent for Osaka. Close friends Madison Keys and Sloane Stephens meet in another eye-catching first-round match.

There will be no Serena or Venus Williams at the final major of the year due to injuries.

Top seed Elina Svitolina had no trouble booking her spot in the Chicago Women's Open quarter-finals on the same day Venus Williams and Sofia Kenin pulled out of the US Open.

Svitolina made light work of Fiona Ferro on Wednesday, cruising to a 6-4 6-4 victory at the WTA 250 tournament.

The Ukrainian star and bronze medallist at the 2020 Olympic Games in Tokyo will face seventh seed Kristina Mladenovic in the quarters.

Marketa Vondrousova – the fifth seed, ninth seed Alize Cornet, Tereza Martincova and Rebecca Peterson also moved through from the round of 16.

At Tennis in the Land, second seed Anett Kontaveit secured a quarter-final berth by topping Caroline Garcia 6-3 6-3 in Cleveland.

Meanwhile, Williams and Kenin withdrew from next week's US Open at Flushing Meadows.

Williams – a two-time US Open champion – will not compete in New York due to a persistent leg injury, joining sister Serena in sitting out the year's final grand slam.

"It's super, super, super disappointing," Williams said in a video via her Twitter and Instagram accounts. "I'm having some issues with my leg all this summer, and just couldn't work through it.

"I tried my best here in Chicago [at the WTA 250 Chicago Women's Open], but I just was unable to figure out the equation. And there's been so many times where I've been able to figure it out, even not in the best of my health, but this time, I just couldn't make any miracles work."

Kenin – the 2020 Australian Open champion – withdrew after testing positive for coronavirus.

"Fortunately I am vaccinated and thus my symptoms have been fairly mild," Kenin tweeted. "However I have continued to test positive and thus will not be able to compete at the US Open next week."

"I plan to spend the next several weeks getting healthy and preparing to play well this fall. Thank you all for supporting me. I want to wish all the players the best of luck in New York."

Patrick Mouratoglou says Serena Williams' "heartbreaking" withdrawal from the US Open was the "only possible decision" for the American.

Williams on Wednesday revealed she will not play in her home grand slam due to injury.

The 23-time major champion has not played on the WTA Tour since suffering a torn hamstring at Wimbledon in June and she has not fully recovered.

Mouratoglou, Williams' coach, stated that pulling out of the final slam of the year was the only option for the six-time US Open singles champion.

He tweeted: "Since she had to pull out from Wimbledon, @serenawilliams has been fully committed to her recovery and we've done everything we could so that she could compete at the @usopen. But her body isn't ready. It is heartbreaking, but this is the only possible decision."

Williams posted on Instagram earlier in the day: "After careful consideration and following the advice of my doctors and medical team, I have decided to withdraw from the US Open to allow my body to heal completely from a torn hamstring,

"New York is one of the most exciting cities in the world and one of my favourite places to play – I'll miss seeing the fans but will be cheering everyone on from afar. Thank you for your continued support and love. I’ll see you soon."

Williams, who turns 40 next month, is the latest high-profile withdrawal from the tournament after Roger Federer and Rafael Nadal pulled out through injury

It will be the first time since 1997 that the US Open will be played without Williams, Federer or Nadal.

Serena Williams has withdrawn from the US Open after failing to fully recover from a torn hamstring.

The 23-time grand slam champion, who won six of those titles at Flushing Meadows, has not played on the WTA Tour since sustaining the injury at Wimbledon in June.

She skipped last week's Western and Southern Open in the hope of being ready in time for the her home major in New York, but has now taken the decision to pull out of the event.

"After careful consideration and following the advice of my doctors and medical team, I have decided to withdraw from the US Open to allow my body to heal completely from a torn hamstring," Williams posted on her Instagram account on Wednesday.

"New York is one of the most exciting cities in the world and one of my favourite places to play – I'll miss seeing the fans but will be cheering everyone on from afar. Thank you for your continued support and love. I’ll see you soon."

World number one Ash Barty says her Western and Southern Open title holds her in "good stead" ahead of the U.S. Open which starts at Flushing Meadows next Monday.

The Australian defeated unheralded Swiss Jil Teichmann in straight sets in Sunday's final in Cincinnati in the perfect preparation for the U.S. Open.

Barty has never gone further than the fourth round at Flushing Meadows and did not compete in last year's U.S. Open due to COVID-19 concerns.

The 2021 Wimbledon champion, who also won the 2019 French Open crown, looms as a strong favourite for the women's singles title although she is typically refusing to get carried away.

"I think we're just excited that we've got matches under our belt in tough conditions here in Cincy, and that's put us in really good stead going into New York," Barty said.

"This week it was completely 'non-result-focused'. It was about preparing in the best way possible, knowing that we wanted to be ready for New York in a couple of weeks' time.

"Now that we've only got a week in between, we have played plenty of matches, and now it's about kind of refining as best we can to hopefully be feeling good come the first round in New York and just try and do the best that we can there."

On her favouritism, she added: "There are no certainties in sport, no certainties in tennis. It's just about playing each and every day as best you can as they come, and not focusing or concerning yourself or your self-worth with results."

Riding the wave of her Wimbledon triumph, Barty crashed out of the women's singles in the first round at Tokyo 2020 to Spaniard Sara Sorribes Tormo last month.

The Australian remained grounded after her Cincinnati victory and insisted preparations for the U.S. Open would stay normal.

"I think sometimes after big wins - and I felt it both times after the French Open and after Wimbledon - there's been a little bit of a big crash, more emotionally than anything else, because there's so much invested into that event," Barty said.

She added: "Our practice weeks before grand slams are quite normal. There is nothing fancy, no extra emphasis on anything.

"It's just gauged by how I'm feeling physically, how I'm feeling mentally, and we have had a lot of practice now as a team in being able to read each other and what we think is required.

"Then it's about going out there for the first round, whether it's the Monday or Tuesday, and try to do the best that I can. That's all I can ask of myself."

The draw for the U.S. Open will be revealed on Friday with Barty going in as the top women's seed, with Aryna Sabalenka second seed and reigning champion Naomi Osaka third.

Ash Barty won her first Western and Southern Open title on Sunday with a straight-sets defeat of Jil Teichmann in Cincinnati.

The world number one took her tally to 40 match wins and five WTA Tour titles in 2021 with a 6-3 6-1 victory.

Teichmann, ranked 76th in the world, had won all four of her meetings with top-10 players this season and accounted for Naomi Osaka, Karolina Pliskova and Olympic gold medallist Belinda Bencic during this exceptional week.

Beating Barty, however, proved a step too far. The Australian recovered from some early jitters, winning 85 per cent of points behind her first serve and breaking her opponent five times.

Teichmann's resistance faltered as errors saw her fall 5-3 behind in the opener and Barty won eight straight games to take command of the contest.

Barty needed just one match point to see out the victory, the first at Cincinnati by an Australian woman since Evonne Goolagong Cawley in 1973.

"I think being able to come through and play a really clean week and walk away with the title is probably not what I really expected of myself, but [it is] certainly nice," Barty, who did not drop a set all week, told the Tennis Channel.

Barty will be the firm favourite to win the US Open, where she has never before gone beyond the fourth round. The Flushing Meadows grand slam begins on Monday, August 30.

World number one Ash Barty reached yet another final on Saturday at the Western and Southern Open, where she will face wildcard Jil Teichmann.

Barty is through to her sixth title match of the season – and first in Cincinnati – after beating Angelique Kerber in straight sets.

In action on the WTA Tour for the first time since winning at Wimbledon, having gone to the Tokyo Olympics in the intervening period, the Australian came through a sloppy spell in the second set to advance 6-2 7-5.

Teichmann is next, taking on Barty for the first time after a stunning run continued with victory over Karolina Pliskova.

The world number 76 had already eliminated Naomi Osaka and Belinda Bencic and was a deserving 6-2 6-4 winner against Pliskova.

Barty finds the balance

Barty had been racing towards victory when she took the opener on Kerber's serve, her second break, and then went 2-0 up in the second.

But Kerber gave the favourite a scare by winning each of the next three games, belatedly finding joy against the Barty serve.

The All England Club champion has won more matches than any other player on tour this year, though, and regained her composure to break twice more for a 39th triumph of 2021.

"It's never, ever a walk in the park against Angie," Barty said. "She's an exceptional competitor and I think early on in that second set she went to another gear and it took me a few games to go with her.

"That was the change – she was able to lift her game and, even though there were some close games, she won the big points early on in the second set.

"I'm glad that I was able to find a way through there in the end.

"I had to find the balance of being aggressive and not getting too passive and letting Angie dictate.

"She moves exceptionally well, puts the balls in difficult positions, and I felt like when I was able to control the court I did a better job.

"In the games I got broken, she just saw too many second serves and was able to be assertive.

"I'm really happy to get through in the end, and to be playing for a title here in Cincinnati is awesome."

'Random' run wears on

Despite facing three seeds in succession, Teichmann has not dropped a set since losing the first against Osaka in the last 16.

Continuing that sequence against Barty will be a tough ask, but few would have anticipated Pliskova being brushed aside quite so easily.

Teichmann herself has no explanation for a sensational run of form.

"It's tough to explain," she said. "When I ask my coaches what they think of me, they always say, 'You're just an unexpected person, you do random things', so I guess that's one of them.

"I'm feeling really, really good here, the conditions, serving good, moving well, when I can I attack, I defend... What I'm feeling here, I cannot even describe it.

"It's a dream. I'm playing centre court, a final against the world number one. I cannot ask for anything else."

Ash Barty reached her sixth semi-final of the year after winning the battle of grand slam champions against Barbora Krejcikova at the Western & Southern Open.

World number one and top seed Barty – the Wimbledon titleholder – dispatched French Open champion Krejcikova in straight sets in Cincinnati on Friday.

Another slam champion awaits Barty in the form of Angelique Kerber, while wildcard Jil Teichmann continued her fairytale run with victory over Olympic gold medallist Belinda Bencic.

Coffee the tonic for in-form Barty

Australian star Barty was too good for Krejcikova, winning 6-2 6-4 at the WTA 1000 tournament.

Barty had to battle from a break down in the second set against the fast-rising Krejcikova, who has shot up from 65th in the world to a career high of number 10 this year.

After extending her season record to 38-7, Barty talked about the importance of drinking coffee in the morning.

"I travel with a French press and an AeroPress, just to have two options. Usually every tournament we go to, one of us has a cafe that we have been to before, so I have got a little section of all my local cafes from the tournaments, so we try and get out to those if we can," she said.

"This year, some places we haven't been able to; some places we have. It's been nice to get some sort of a mixture, but I'm pretty simple. I'm just a black coffee cup in the morning, and then I'm set."

Three-time major champion Kerber is next up after she was 6-4 3-3 ahead before Petra Kvitova retired hurt due to a stomach problem.

Teichmann takes down another star

Unheralded Swiss and world number 76 Teichmann claimed another scalp, this time upstaging countrywoman Bencic 6-3 6-2 in the quarter-finals.

Teichmann stunned world number two Naomi Osaka en route to the quarters and maintained her giant-slaying form in Cincinnati, where 10th seed Bencic became the latest victim.

"We hugged before the match; we hugged after the match," Teichmann said of the Bencic meeting. "We know that once we step on court it's business, it's just another player I have to deal with, and she had the same mindset. At the beginning it's obviously a bit special, but once we're in it, we just look at the game, not looking at the opponent, or at least I do that way."

Teichmann will take on fifth seed Karolina Pliskova, who advanced to her second successive WTA 1000 semi-final after Paula Badosa retired down 7-5 2-0.

Ash Barty and Angelique Kerber set up a blockbuster Western and Southern Open semi-final – but Petra Kvitova suffered a fitness scare ahead of the US Open.

World number one Barty won 6-2 6-4 against French Open champion Barbora Krejcikova, who she also defeated in the fourth round during her Wimbledon title run last month.

Kerber and Kvitova then battled it out for the right to tackle Barty in the last four, but a quarter-final that was building momentum ended prematurely when two-time Wimbledon winner Kvitova found a recent stomach problem too troublesome.

Kerber was 6-4 3-3 ahead in the contest, having recovered from being an early break down in the second set, getting her game together as 31-year-old Kvitova began to suffer.

During an injury timeout, which Kvitova called after the fifth game of the second set, the Czech received a massage to her abdominal region and played on briefly, before walking up to the net to concede the match.

It remains to be seen whether the setback in Cincinnati might have consequences for her involvement at Flushing Meadows, with the US Open due to begin on August 30.

Kvitova wrote on Twitter minutes after coming off court: "I stayed out there as long as I could. I have been struggling with a stomach issue for several days and unfortunately couldn't finish the match today. Good luck Angie - sorry to end it that way - and can't wait for the next battle with you."

Kerber said in an on-court interview: "Of course, this is not the way you would want to win the match. I hope Petra will recover as fast as possible and be ready for the US Open.

"I know she's a big fighter and fights until the last points, so I hope she is not too bad and hope she is fine really, really soon."

Kerber has now won 14 of her last 15 matches, with the exception being her Wimbledon semi-final defeat to Barty.

Barty got through in a more routine manner on Friday, albeit having to battle from a break down in the second set against the fast-rising Krejcikova, who has shot up from 65th in the world to a career high of number 10 this year.

Barty said: "Barbora served exceptionally well early in that second set and was able to take advantage of a service game of mine where I just hit too many second serves.

"I wanted to try and get a little bit more positive on her service games and then try to get myself in the points a little bit more. I'm happy to run away with that one in the end."