TORONTO - Serena Williams' first U.S. Open tune-up ended in dramatic fashion as the tearful American was forced to retire with a back injury while trailing Canadian teenager Bianca Andreescu 3-1 in the Rogers Cup final on Sunday.

Williams, who hopes to chase a record-equalling 24th career Grand Slam title at the U.S. Open, seemed fine on court but suddenly sat crying in her chair before deciding to retire 19 minutes into the match with back spasms.

"I'm sorry I couldn't do it today. I tried but I just couldn't do it," an emotional Williams, who struggled to get the words out, told the crowd.

"It's been a tough year but we'll keep going."

Andreescu consolidated an early break to move 3-1 up at which point Williams went to her chair where she called for the trainer and broke down in tears.

Williams said the spasms began during her three-set semi-final win over Czech Marie Bouzkova on Saturday. They got so bad that she was unable to sleep and could not really move but she added that she at least wanted to try and play the final.

"I was just trying to figure out how do you play a match where you have no rotation?" said Williams.

"And I don't want to get this far and not at least try. I think I would have really regretted not at least going out there and seeing maybe if a miracle happened."

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The 37-year-old Williams, whose competitive action this year has been severely limited because of knee issues, declared herself pain-free ahead of the tournament, which she was hoping to use as a springboard for the rest of her hardcourt swing.

But the six-times U.S. Open champion, still without a title since returning from maternity leave in 2018, now faces her latest injury setback with the year's final Grand Slam just two weeks away.

Williams, who is due to compete in Cincinnati next week, said she has experienced back spasms a lot in her career and that if this latest episode plays out like those before, she does not expect it to keep her out of any events.

"They're incredibly painful, but it goes away after, like, 24, 36, maybe 48 hours, and like clockwork," said Williams.

"In that first phase, it is incredibly painful, to a point where I usually don't get out of bed. So if it's what typically happens, I will be fine, but I have to wait and see."

As Williams sat dejected in her chair, Andreescu, who is no stranger to injury setbacks, went over to console her. The pair embraced and had a heartfelt conversation.

Andreescu, who shot to prominence with her Indian Wells triumph in March and was competing this week for the first time since withdrawing from the French Open with a shoulder injury, is the first Canadian to win the event in 50 years.

"I feel for Serena so much. I've been through so much the last year with injury so I am so sorry she had to go out this way," the 19-year-old said during the trophy ceremony.

"Sometimes, you can't push your body and she couldn't today and I wish her a fast recovery."

(Reporting by Frank Pingue in Toronto; Editing by Ian Chadband)

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