Serena Williams rebounded from her worst loss in 16 years by crushing Canada's Eugenie Bouchard 6-1 6-1 at the WTA Finals.
The win keeps alive Williams's hopes of reaching the semi-finals and ends Bouchard's campaign in Singapore.
However, the American will be eliminated if Ana Ivanovic beats Simona Halep in straight sets on Friday.
Halep beat Williams 6-0 6-2 on Tuesday and becomes the first player to qualify for the semi-finals.
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Bouchard, who had lost her first two matches in the Red Group, recovered from 0-40 down in the opening game of the match to hold serve.
But it proved to be a false dawn for the world number five as a dominant Williams reeled off six straight games to take the first set.
Williams continued to overpower Bouchard in the second set and wrapped up victory in less than an hour.
"Yesterday was tough but I really had to put that behind me," Williams said. "My coach really helped me.
"He told me 'You're still in the tournament', even though I felt like I was out of the tournament."
Meanwhile, in the White Group, Caroline Wozniacki moved closer to securing her place in the semi-finals with a 7-5 6-3 victory over Agnieszka Radwanska.
The Dane recovered from 3-0 down to snatch the opening set, and then clinched the match in the second with a run of four straight games.
"I just kept fighting for every point," said Wozniacki, who beat Maria Sharapova in her opening match.
"I've been pleased with the way I've been running a lot of balls down and taking advantage of the important points."
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In the other match in that group, Petra Kvitova beat Maria Sharapova 6-3 6-2 to leave the Russian's chances of qualifying for the semi-finals hanging by a thread.
It was the Czech's first success against Sharapova in their last six meetings.
"Everything I did today was really good," Wimbledon champion Kvitova said. "I'm glad that I beat her and I have still a chance to go to the semi-final."
The result means Williams is all but certain to finish the year as world number one, with current number two Sharapova now needing an improbable sequence of results to overtake her.