Serena Williams

Yesterday, Williams played only her second singles match since she returned to action at Wimbledon in June after a year-long absence from competition, beating Spain's Nuria Parrizas Diaz to reach the second round of the Toronto Open.

But the 40-year-old said after the match that she could see the light at the end of the tennis tunnel in her career.

"I have never liked the word retirement," Williams wrote in a Vogue article.

The American great, 40, returned to the same Centre Court where she had limped out injured last year with a passionate display in a 7-5 1-6 7-6 (10-7) defeat.

Willed on by a fervent crowd, Williams answered questions over her fitness with a dynamic display that put her two points from a win before Tan edged it.

The burning question now is surely 'was this her last Wimbledon'?

"That's a question I can't answer," she told a news conference. "I don't know.

"Who knows? Who knows where I'll pop up."

American Williams, 40, plays France's Harmony Tan on Centre Court, 12 months on from tearing her hamstring in her first-round match at SW19.

Women's world number one Iga Swiatek opens play on the main show court against Croat Jana Fett from 13:30 BST.

Men's second seed Nadal, a two-time winner, then meets Francisco Cerundolo.

A 23-time Grand Slam singles champion, Williams made her long-awaited return to action in the doubles at Eastbourne last week alongside Ons Jabeur, after ending speculation over her future in the sport by accepting a Wimbledon wildcard.

Peng, 35, has not been heard from since she made sexual assault allegations against a leading Chinese government official two weeks ago.

Chinese state media has released an email attributed to Peng, but doubt has been cast about its authenticity.

"I hope she is safe and found as soon as possible," said Williams.

Concern for Peng's welfare has continued to grow since she said she was "forced" into a sexual relationship with former China vice-premier Zhang Gaoli.

In a post on social media, the 39-year-old American great said she needed time to allow her body to "heal completely" from a torn hamstring.

Williams joins defending men's champion Dominic Thiem, plus Roger Federer and Rafael Nadal, in pulling out of this year's final Grand Slam.

The tournament, at Flushing Meadows in New York, begins on 30 August.

Williams wrote on Instagram: "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 started against Belarusian world number 100 Aliaksandra Sasnovich with heavy strapping on her right thigh and then slipped in the fifth game.

The 39-year-old went down again in the seventh game and then retired after struggling to get to her feet.

"I'm so sad for Serena. She is a great champion," said Sasnovich.

"It happens sometimes in tennis, but all the best to her."

Williams, seeded sixth, seemed to do the damage when she rocked backwards on the baseline before unleashing a forehand back to her opponent.

In an absorbing match, the 23-time Grand Slam winner was outmuscled by the Kazakh, who will now seek to take advantage of an open women's draw.

The American tried to lift her level but instead became the latest top-10 seed to depart the women's singles.

Her next chance to equal Margaret Court's record of 24 Grand Slam singles titles comes at Wimbledon from 28 June.

"It was definitely close," Williams said. "There is literally a point here, a point there, that could change the whole course of the match.

The American seventh seed beat compatriot Collins 6-4 6-4 and will face Kazakhstan's 21st seed Elena Rybakina next.

Williams, 39, is one of just four top 10 seeds left in the women's draw after Aryna Sabalenka lost earlier on Friday.

The Belarusian third seed was beaten 6-4 2-6 6-0 by Anastasia Pavlyuchenkova.

Williams is bidding to equal Margaret Court's record of 24 Grand Slam triumphs, but has not made it past the fourth round at Roland Garros since 2016.

Playing her first competitive match in nearly three months, the 23-times Grand Slam champion twice came back from a break down but struggled on her first serve.

Defeat for Williams, who received an opening round bye in Rome, was a major blow to her preparations for the French Open, starting on May 30.

It was the American's 149th defeat in her 1,000 career WTA matches.

World number two Naomi Osaka also crashed out of the tournament, losing to American Jessica Pegula.

American Williams, 39, has rediscovered her best form at Melbourne Park but faces a tough test against Osaka.

She has not played Osaka at a Grand Slam since the Japanese beat her in a dramatic 2018 US Open final.

The match was overshadowed by Williams' argument with umpire Carlos Ramos.

Williams called the umpire a "thief" after he deducted a point from her, and Osaka was reduced to tears by the crowd booing during the presentation ceremony.

"I think we both have had closure, and we have reached out to each other," Williams said of the match.