Williams assured of No 1 spot

Singapore - Maria Sharapova's hopes of becoming the year-end world number one faded dramatically on Thursday when she crashed in straight sets to Petra Kvitova at the WTA Finals in Singapore.

The Russian superstar needed a win to boost her chances of overtaking top-ranked Serena Williams but she blew up in spectacular fashion as Kvitova won 6-3, 6-2 in 75 minutes.

It was the second upset in quick succession at the season finale after Simona Halep stunned Williams 6-0, 6-2 on Wednesday, the 18-time Grand Slam-winner's worst defeat in 16 years.

To finish the year as world number one for the first time in her career, Sharapova, 27, now needs to win the end-of-season championship and hope Williams doesn't reach the final.

But her first loss to Kvitova since 2011 left her campaign hanging by a thread as she sits bottom of White Group with one round-robin match left against Agnieszka Radwanska.

It was a very different story for Caroline Wozniacki, who beat Sharapova on Tuesday, as she downed Radwanska 7-5, 6-3 to near a spot in the semi-finals.

Sharapova won the first two games against Kvitova but then went to pieces as the Wimbledon champion won the next five straight and took the first set 6-3.

Another run of five games put Kvitova on the verge of victory before Sharapova finally 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.

Wozniacki took more than three hours to beat Sharapova on Tuesday and another long match looked likely when she 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 step towards her first semi-final at the year-ender since 2009.

"I knew from the start that this wasn't going to be an easy match," Wozniacki said.

"I came out there a little bit nervous, but you know, I just did my best out there," added the world number eight.