Rogers Cup champion Agnieszka Radwanska defeated Wimbledon title holder Petra Kvitova in straight sets 6-2 6-3 at the WTA Finals in Singapore on Tuesday.

The 25-year-old Polish star was out to prove critics wrong in the first set as she jumped all over the Wuhan Open champion and broke Kvitova twice in five attempts to easily take the first set.

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The third seeded Kvitova staged a comeback in the second set as she broke Radwanska to take a 4-3 lead but the Krakow native would not be denied as she broke back twice to win the match in an hour and 29 minutes.

This is Radwanska's second win over Kvitova in seven outings with the first one two years ago at the same WTA Finals in Istanbul.

"She's a great champion and playing some amazing tennis, especially the last few months, so I'm really happy with that win," Radwanska said. "There's only eight of us here, so you have to go out and try your best, otherwise you're not going to win. And I'm very happy with the way I played tonight."

Both Kvitova and Maria Sharapova, who earlier was outlasted by Caroline Wozniacki in an epic three setter, were favored to battle it out in Group White but have been humbled instead.

"Yeah, I think probably we were both favorites in our matches and of course in our group," Kvitova said. "That's what happens in tennis. I know that Caro beat her in US Open, so she knew it would be difficult."

Defending champion Serena Williams will battle it out against Simona Halep on Wednesday for the top spot of Group Red while Eugenie Bouchard and Ana Ivanovic will try to keep their hopes alive for a final showdown on Friday.

Group White will take a day off and resume their second match in the round-robin stage.