SINGAPORE - Serena Williams hit back from her embarrassing defeat at the WTA Finals by demolishing Eugenie Bouchard 6-1, 6-1 to keep her campaign alive in fearsome fashion on Thursday.

After only winning two games against Simona Halep, a grimly focused Williams only lost two against Bouchard as she swept the glamorous Canadian off court and out of the tournament in 58 minutes. The defending champion lost the first game but then grabbed 11 in a row, including a serve recorded at 205 kilometres (127.4 miles) an hour in the second set, not far off Sabine Lisicki's world record. It was exactly the response needed from the world number one after Wednesday's 6-0, 6-2 loss to Halep -- her heaviest since 1998 -- put the skids under her attempt at a third straight year-end title.

"Yesterday was tough for me but I had to put that behind me," Williams said. "My coach told me I was still in the tournament, even though I felt like I was out of the tournament." Despite the big victory, Williams will still crash out if Halep fails to win a set against Ana Ivanovic in the final Red Group round robin match on Friday. Bouchard departs after her third defeat.

Earlier, Maria Sharapova slumped 6-3, 6-2 to Petra Kvitova as both her title hopes, and her chances of overtaking Williams and finishing the year as world number one, receded dramatically. The Russian superstar, also beaten in her opener against Caroline Wozniacki, now needs to win the end-of-season championship and hope Williams doesn't reach the final to become year-end number one. But her first loss to Kvitova since 2011 left her campaign hanging by a thread as she sits bottom of White Group with two defeats and one round-robin match left against Agnieszka Radwanska.

"Of course I had a long match, over three hours a day ago, but I don't feel tired," said Sharapova, who went down in three tough sets to Wozniacki."I'm happy to be here, I'm happy to be part of this event. It's easy to sit here and say, 'Yeah, I'm tired'. I lost two matches. But that's not the way I feel or the way that I choose to speak." Sharapova won the first two games against Kvitova but then went to pieces as the Wimbledon champion grabbed the next five and took the first set 6-3.

Another run of five games put Kvitova on the verge of victory before Sharapova earned a break of her own, and then saved two match points as she clung on in a 10-minute hold of serve at 5-1 down. However, her resistance was broken when on the third match point, Kvitova blasted a magical looping forehand which landed on the baseline and beyond the crestfallen Russian. Elsewhere, a repeat of Wozniacki's epic against Sharapova looked on the cards when the Dane fought with Radwanska in a tight opening set which featured five breaks of serve. But the super-fit former world number one, who is training for the New York marathon, raced through the second set to win 7-5, 6-3 and close on a spot in the semi-finals.