Simona Halep's former coach Darren Cahill has jumped to the Romanian's defence after the former Wimbledon and French Open champion failed a drug test.

Cahill said Halep's "integrity is faultless" and insisted there was "no chance" she would have deliberately or wittingly taken a banned substance.

It was made public on Friday that 31-year-old Halep tested positive for roxadustat while competing at the US Open in August.

Halep, who has been provisionally suspended, said she felt "confused and betrayed" by the news. She has not explained why, or by whom, she senses a betrayal.

She now risks a ban from tennis and faces a battle to clear her name, which she has said she is determined to achieve.

Cahill was Halep's coach when she landed her first grand slam title at Roland Garros in 2018, and he pointed to his experience of an athlete who was meticulous about checking anything she ingested.

He wrote in a statement posted on Instagram: "Firstly, and most importantly, there is NO chance Simona knowingly or purposely took any substance on the banned list. None. Zero.

"She is an athlete that stressed about anything prescribed to her by a medical professional [which was rarely], or about any supplement that she used or considered. Simona wore out the words 'please double check this, triple check this to make sure it’s legal, safe and permitted. If you are not sure, I'm not taking it.'"

Australian Cahill has also worked with players including Lleyton Hewitt, Ana Ivanovic, Andy Murray and Andre Agassi. He rates Halep as a player and person of the highest order.

When they stopped working together in September 2021, Halep thanked Cahill "for making me a better tennis player and a better person".

Cahill wrote on Sunday: "Simona's integrity is faultless, she respects her peers, she loves the game and she always has her feet firmly planted on the ground as a humble, approachable champion.

"Honesty has always been her greatest strength and her biggest weakness. We would often laugh about the fact that she can't act and can't tell a little white lie.

"She wears her mood on her shoulder for the world to see, for good and for bad. That is Simo. What you see is what you get. She built an amazing career and legacy by doing things the hard way. The right way.

"Due process will now follow to reveal answers to many questions. As Simona said, the hardest match of her life starts now. I believe in her. I always have and can honestly say never more than right now on this particular issue. I stand with Simo."

Simona Halep said she felt "confused and betrayed" after being handed a provisional suspension for failing a drug test.

The International Tennis Integrity Agency announced on Friday the 31-year-old had tested positive for roxadustat, a prohibited substance, after providing two samples while competing at the US Open in August.

She was notified of a rule violation on October 7 and now faces a fight to avoid a ban from the sport.

In a statement, the ITIA said: "While provisionally suspended, the player is ineligible to compete in or attend any sanctioned tennis event organised by the governing bodies of the sport."

Swiftly responding, former French Open and Wimbledon champion Halep denied all knowledge of taking the substance and said the sanction was the "biggest shock" of her life.

"Today begins the hardest match of my life: a fight for the truth," she posted on social media.

"I have been notified that I tested positive for a substance called roxadustat in an extremely low quantity, which came as the biggest shock of my life.

"Throughout my whole career, the idea of cheating never even crossed my mind once, as it is totally against all the values I have been educated with. Facing such an unfair situation, I feel completely confused and betrayed.

"I will fight until the end to prove that I never knowingly took any prohibited substance and I have faith that sooner or later, the truth will come out.

"It's not about the titles or the money. It's about honour, and the love story I have developed with the game of tennis over the last 25 years."

The 31-year-old former world number one announced in September she would miss the rest of the season after undergoing nose surgery, with it unclear how long her recovery would take.

Simona Halep has announced her season is over after undergoing nose surgery to address problems with her breathing.

Working with Serena Williams' former coach Patrick Mouratoglou, Halep enjoyed a promising 2022 following an injury-hit 2021 campaign, reaching the semi-finals at Wimbledon and moving up to ninth in the WTA rankings.

However, the two-time major champion has struggled since winning the Canadian Open last month, losing in the first round at the US Open.

Prior to her success in Canada, Halep was forced to retire in the second round of the Citi Open after enduring breathing difficulties, and the ongoing problem prompted surgery this week, with Halep disclosing she also elected for cosmetic changes to the nose.

The former world number one will miss the final events on the WTA Tour this year, but she explained the procedure was necessary.

She wrote on Twitter: "As you all know already because I've talked about it many times, in February, I was very close to stopping tennis because I didn't believe I have enough power to come back to top 10. I was going through many anxious moments and I thought it is time to stop cause it is emotionally unhealthy. 

"Then I was lucky to discover Patrick's academy where I felt so much passion that it gave me back my passion for tennis. Thanks to Patrick, I slowly started to believe that I still can play a good level of tennis.

"My goal was very clear: I gave myself one year to get back to top 10. And faster than I ever expected, in only two months, I was back to top 10. Goal achieved!

"But then, when I lost at the US Open, I realised that I'm completely exhausted mentally. Having problems with the breathing for many years already and becoming worse with the time, I decided to follow the advice of my doctors and do the needed surgery.

"I could never do it earlier because I never found the necessary three months for the recovery, because tennis was always the first priority in my life. But I felt it's the right time to do it and also to do something for myself as a person.

"That is why I did also the aesthetic part, that I wanted to do for a long time as I did not like my nose at all. So I did it, I solved the functional part and the aesthetic part.

"I don't know how long the recovery will take, for the moment I am not thinking about anything but recovery. What is sure, is that this year I won't be able to compete in any official tournament anymore.

"My 2022 season is over. 2022, you have been an interesting year full of everything! See you on court, 2023! I feel I still have a lot to do on a tennis court and still have some goals."

Ukrainian qualifier Daria Snigur dedicated her shock victory over Simona Halep in the opening round of the US Open to the people in her war-torn country.

The world number 124 marked her debut in the main draw of a major with a 6-2 0-6 6-4 win at Flushing Meadows on Monday.

Snigur is the lowest-ranked player to win a grand slam match against Halep – one of the favourites for the title – since Maria Sharapova at the same tournament in 2017.

She is also the first female qualifier to win a US Open match against a top-10 seed since Johanna Konta eliminated Garbine Muguruza seven years ago.

Making Snigur's achievement all the more incredible is that the 20-year-old's training base in Kyiv was bombed by Russia, forcing her to instead prepare for the event in Riga.

Reflecting on the biggest win of her burgeoning career, a tearful Snigur said: "This is a victory for Ukraine, for all Ukrainian people, for my family, for my team.

"The situation is bad, of course. I try to do the best for Ukraine, I try to support my country.

"It's not so easy because the war is continuing. Sometimes it's impossible to play but I try to do my best because I want to live in Ukraine.

"I have to say thanks to Simona for this incredible match. I want to thank all the fans who watched our match today."

Two-time major champion Halep has lost just three of her past 19 first-round matches in grand slams, though each of those have come at the US Open.

Snigur will now face Rebecca Marino, who defeated Magdalena Frech in straight sets to advance to the second round.

Simona Halep was the first big casualty at the US Open when she was sensationally beaten by qualifier Daria Snigur on day one.

Halep arrived at Flushing Meadows as one of the favourites to win the title after she was crowned Canadian Open champion this month.

The two-time grand slam champion fell at the first hurdle, though, as Ukrainian Snigur consigned her to a stunning 6-2 0-6 6-4 defeat on Louis Armstrong Stadium.

Making her first appearance in the main draw at a major, the unheralded 20-year-old was rewarded for a positive approach, winning eight out of 12 points at the net and breaking five times.

Halep swept the world number 124 aside in the second set, but the outsider claimed the upper hand with break in the first game of the decider and went on to open up a 5-1 lead.

The former world number one showed her fighting spirit to hang in there, reducing the deficit to 5-4, but Snigur demonstrated nerves of steel to serve out the match and looked as shocked as anyone after sealing her place in the second round in New York.

Halep paid the price for 30 unforced errors, crashing out after a run to the semi-final in the last major at Wimbledon.

Simona Halep secured victory against Beatriz Haddad Maia in the Canada Open final on Sunday, though was given a tougher test than she had otherwise experienced throughout the tournament.

The Romanian was a 6-3 2-6 6-3 victor, dropping a set for only the second time in the week, but standing firm in the clash that clocked in at over two hours.

That meant records for Haddad Maia, who has played the most WTA-level matches with three sets in 2022 (20) and spent over 12-and-a-half hours on the court at the Canada Open in 2022, more than any other player in a single WTA tournament this year.

Wimbledon semi-finalist Halep proved to be a step too far for the Brazilian, however, with the win marking her most significant honour since winning in Rome in 2020.

It was far from a vintage performance from the 30-year-old, who had nine double-faults in the match compared to Haddad Maia's two and left the door open for the South American - who was vying for victory in her first ever WTA 1000 event.

Halep had already clinched a return to the world top 10 by reaching the final in Toronto, the first time since her 373-week stint ended just over a week ago - which led to admissions that she considered calling it quits amid her decline.

A valiant comeback in 2022 has been one of the major stories of the calendar year though and, on the back of victory in Canada and a semi-final march at Wimbledon, will have high hopes for the U.S. Open.

Simona Halep came from a set behind to defeat seventh seed Jessica Pegula 2-6 6-3 6-4 in the semi-final of the Canadian Open on Saturday, booking her place in the final against Beatriz Haddad Maia.

Romania's Halep, the 15th seed, struggled to return Pegula's serve in the opening set, winning just 32 per cent (nine-of-28) of her return points while compounding her early issues with four double faults.

Whether Pegula began to run out of steam, or Halep figured something out, she had significantly more success against the American's serve the rest of the way, winning 55 per cent (12-of-22) of her return points in the second set, and 57 per cent (20-of-35) in the decider.

Halep has now won 11 of her past 13 matches, and Pegula is her third consecutive win against a top-25 opponent after defeating both world number 21 Jil Teichmann and world number 13 Coco Gauff in straight sets. 

While this will be Halep's 18th career WTA 1000 final, it will be Haddad Maia's first, after she emerged triumphant 6-4 7-6 (9-7) against 14th seed Karolina Pliskova.

She did not have a serving advantage against Pliskova, who won the ace count nine-to-one, but she was gritty, saving four of the six break points she faced, and refused to concede the second set after dropping the first three games.

Haddad Maia – the only Brazilian ranked inside the top-100 – has now beaten five consecutive top-25 opponents on her way to the final, including world number one Iga Swiatek, Olympic gold medalist Belinda Bencic and Canadian hometown hero Leylah Fernandez.

Two-time major winner Simona Halep continues to find form ahead of the upcoming US Open with a 6-4 7-6 (7-2) victory over Coco Gauff clinching her spot in the Canadian Open semi-finals.

Halep defeated 10th seed Gauff, who had beaten Naomi Osaka, Elena Rybakina and Aryna Sabalenka this week, in one hour and 47 minutes.

The Romanian 15th seed was broken five times and sent down eight double faults, but found the edge with speed, finesse and power.

The win means Halep has won the third most matches (36-10) on the WTA Tour this season, behind only top-ranked Iga Swiatek (49) and Wimbledon finalist Ons Jabeir (37).

Halep's improved form comes after she teamed up with Serena Williams' ex-coach Patrick Mouratoglou in April following a difficult 2021 season.

"Before I met him I was super down with my motivation," Halep told reporters. "I couldn't really work, keep working. I was almost done with tennis. He brought this fire back and the motivation. He trusted that I still can play good tennis and he transferred this to me."

The 2018 French Open and 2019 Wimbledon champion added: "Physically I'm good. Mentally I'm good, so I think it's all positive."

Halep, who won the Canadian Open in 2018, has reached the semi-finals for the fifth time in her career where she will take on seventh seed Jessica Pegula.

Pegula got past Yulia Putintseva 6-3 6-3 in one hour and 21 minutes. Qualifying for the last four at the Canadian Open for the second straight year.

Brazilian Beatriz Haddad Maia maintained her Canadian Open run, having ousted Swiatek in the third round and local favourite Leylah Fernandez in the second, with a 2-6 6-3 6-3 victory over Tokyo Olympics gold medalist Belinda Bencic in two hours and 11 minutes.

Haddad Maia became the first Brazilian to reach the semi-finals of a WTA 1000 tournament. She will face Karolina Pliskova in the semi-finals after the Czech 14th seed beat Qinwen Zheng 4-6 6-4 6-4.

Coco Gauff will reach the highest ranking of her career after the 18-year-old defeated world number six Aryna Sabalenka 7-5 4-6 7-6 (7-4) in the third round of the Canadian Open on Thursday.

Gauff, who has never been ranked higher than her current spot of 11th, will overtake Emma Raducanu and likely Daria Kasatkina to move up to ninth when the next rankings are released after prevailing in an exceptionally tight match against her Belarussian opponent. 

Incredibly, both Gauff and Sabalenka won exactly 131 points each, posting identical success rates on service points (77-of-131) and return points (54-of-131).

Gauff will be considered one of the favourites in the tournament after world number one Iga Swiatek was sensationally eliminated by Brazil's Beatriz Haddad Maia. Swiatek was sloppy, committing nine double faults to just one from her opponent.

Two-time grand slam winner Simona Halep defeated rising Swiss talent Jil Teichmann 6-2 7-5, utilising her dominant first serve to get the job done. Halep converted 82 per cent (32-of-39) of her accurate first serves into points, compared to just 59 per cent (29-of-49) for Teichmann.

World number seven Jessica Pegula had to save a match point on her way to a comeback 3-6 6-0 7-5 win against reigning Canadian Open champion Camila Giorgi, booking her quarter-final clash against Yulia Putintseva after the Kazakhstani beat Alison Riske 6-3 7-5.

Third seed Maria Sakkari went down 1-6 7-6 (11-9) 3-6 against 14th seed Karolina Pliskova, and the Czech will take on China's Qinweng Zheng after she eliminated Canada's last remaining contender Bianca Andreescu 7-5 5-7 6-2.

In the final match of the night, Tokyo Olympics gold medalist Belinda Bencic was incredibly impressive against world number eight Garbine Muguruza, prevailing 6-1 6-3.

The Serena Williams' farewell tour in Toronto is over after she was knocked out of the Canadian Open 6-2 6-4 by 12th seed Belinda Bencic on Wednesday.

Williams, playing for the first time since declaring on Tuesday her intention to retire after this month's US Open, was no match for Tokyo Olympics gold medalist Bencic.

The 23-time major winner was unable to claim back-to-back WTA singles wins for the first time since last year's French Open, having defeated Nuria Parrizas-Diaz for her first victory in 430 days on Monday.

Bencic triumphed in one hour and 17 minutes, winning 84.2 per cent of first-serve points and converted five of eight break points throughout the match.

Williams' power was on show with 13 winners, but Bencic was physically more capable and decisively managed 25 winners with only 13 unforced errors.

Elsewhere, 2019 US Open winner and local hope Bianca Andreescu edged Alize Cornet in a see-sawing clash in the evening, winning 6-3 4-6 6-3 in two hours and 26 minutes.

Fourth seed Paula Badosa and fifth seed Ons Jabeur, who was last month's Wimbledon runner-up, were forced to retire due to injury.

Spanish 24-year-old Badosa withdrew against Yulia Putintseva 7-5 1-0 due to muscle cramping, while Zheng Qinwen had a walkover against Jabeur 6-1 2-1 due to abdominal pain.

Top seed Iga Swiatek brushed aside Ajla Tomljanovic 6-1 6-2 in 64 minutes. The win means Swiatek is the first player to win 15 WTA 1000 matches in straight sets in a row since 2009.

Canadian 13th seed Leylah Fernandez also bowed out, going down 7-6 (7-4) 6-1 to Brazil's Beatriz Haddad Maia, who will face Swiatek in the third round.

Second seed Anett Kontaveit lost 6-4 6-4 to Jil Teichmann in one hour and 27 minutes. Teichmann will next face Simona Halep who won in 71 minutes against Zhang Shuai 6-4 6-2.

Sixth seed Aryna Sabalenka got past Sara Sorribes Tormo 6-4 6-3 to set up a third-round meeting with Coco Gauff after she defeated Wimbledon champion Elena Rybakina 6-4 6-7 (8-10) 7-6 (7-3) in an epic that lasted two hours and 49 minutes.

Jessica Pegula won 6-2 7-5 over American qualifier Asia Muhammad to progress through to face Camila Giorgi after she knocked off Elise Mertens 7-3 7-5.

Third seed Maria Sakkari triumphed in three sets 6-2 4-6 6-2 over Sloane Stephens and will face Karolina Pliskova next after the Czech beat Amanda Anisimova 6-1 6-1.

Eighth seed Garbine Muguruza won 6-4 6-4 against Kaia Kanepi and Alison Riske toppled 16th seed Jelena Ostapenko 7-6 (7-2) 0-6 7-5.

Serena Williams highlighted the first day of the Canadian Open, defeating Nuria Parrizas-Diaz 6-3 6-4 for her first win since the 2021 French Open.

In doing so, Williams became the fourth player since 2000 to win a WTA-level main draw match after turning 40, joining sister Venus Williams, as well as Kimiko Date Krumm and Martina Navratilova.

She also claimed the all-time record for wins at the Canadian Open, with 35, now one more than Chris Evert.

"I guess there’s just a light at the end of the tunnel," Williams said after the match. "I don’t know, I’m getting closer to the light. Lately that's been it for me. I can’t wait to get to that light."

She added: "I love playing though, so it’s like amazing. But I can’t do this forever. Sometimes you just want to try your best to enjoy the moments and do the best that you can."

Williams' older sister Venus, 42, was beaten on Monday by Swiss Jil Teichmann 6-2 6-3 with the match finshing after midnight following a delayed start due to rain.

One of the three seeded players in action on Monday, 15th seed Simona Halep had no issues cruising through the challenge of Donna Vekic 6-0 6-2.

It was similarly smooth sailing for 14th seed Karolina Pliskova in her all-Czech showdown against Barbora Krejcikova, winning 6-3 6-4, while Latvian 16th seed Jelena Ostapenko handled the challenge of Ukraine's Anhelina Kalinina 6-4 6-2.

Kazakhstan's Elena Rybakina defeated in-form qualifier Marie Bouzkova 7-5 6-7 (3-7) 6-1, likely earning a shot at Coco Gauff if the American wins as a heavy favourite tomorrow, while Brazil's Beatriz Haddad Maia beat Italy's Martina Trevisan 6-2 2-6 6-2 in a meeting of two top-30 players.

In a pair of all-American battles, Sloane Stephens edged Sofia Kenin 6-2 7-6 (7-5) 7-5, and world number 187 Asia Muhammad upset world number 25 Madison Keys in straight sets 7-6 (7-5) 6-4.

Alize Cornet defeated her French compatriot Caroline Garcia 3-6 6-3 6-3, and Canada's Katherine Sebov was unable to get the job done in front of her home fans, going down 6-3 2-6 5-7 to Yulia Putintseva.

In better news for the Canadians, Leylah Fernandez won 6-4 6-7 (2-7) 6-3 over Storm Sanders, while veteran two-time Wimbledon winner Petra Kvitova was beaten by Alison Riske 6-2 4-6 6-3.

Second and third seeds Paula Badosa and Ons Jabeur eased into the Silicon Valley Classic quarter-finals on Wednesday, while Simona Halep and Jessica Pegula were bundled out of the Citi Open.

Last month's Wimbledon finalist Jabeur proved too good for American Madison Keys 7-5 6-1, winning in one hour and 22 minutes.

Jabeur, playing for the first time since Wimbledon, converted six of nine break points for the match, dominating the second set where she won 90.9 per cent first serve points.

Second seed Badosa survived a scare to win over qualifier Elizabeth Mandlik 6-2 5-7 7-6 (7-5) in two hours and 31 minutes.

Eighth seed Karolina Pliskova was knocked out by American Amanda Anisimova 3-6 7-5 6-1, while last year's runner-up Daria Kasatkina beat Taylor Townsend 6-4 6-0.

Two-time major winner Halep was forced to retire due to illness and top seed Jessica Pegula was bundled out by Daria Saville at the Citi Open.

In warm conditions, the 30-year-old Romanian battled throughout the match but eventually retired down 7-5 2-0 to Anna Kalinskaya after one hour and six minutes.

Halep had fought back from a 4-0 deficit in the first set to square it up at 5-5, before losing the first set.

However, the former world number one succumbed to illness early in the second set, handing Kalinskaya her passage into the quarter-finals.

On a dramatic day for the Citi Open favourites, world number seven Pegula was eliminated by Saville in straight sets in one hour and 38 minutes, 7-5 6-4.

Pegula was not helped by a first-serve percentage of 44.8 per cent, while she struggled to convert break points, with the Australian saving nine of 10 for the match.

Saville's win means she is 3-3 against top 20 opponents this year, progressing into the last eight where she will face Canadian qualifier Rebecca Marino.

Marino, who beat Venus Williams in her return to singles in the first round on Monday, knocked off Germany's Andrea Petkovic 6-3 3-6 6-1.

Estonian sixth seed Kaia Kanepi progressed into the quarters where she will face Kalinskaya after beating China's Zhu Lin 4-6 6-4 6-4.