ISTANBUL (AP) Top-ranked Caroline Wozniacki rallied past Agnieszka Radwanska 5-7, 6-2, 6-4 Tuesday in their opening round-robin match at the WTA Championships.

Wozniacki wasted a 4-2 lead in the third set but broke again when Radwanska netted a forehand on the Dane's second match point.

Radwanska converted both her break points to take the first set. The second set featured six breaks of serve, with Wozniacki getting four.

``It was a bit frustrating not to get the first set after having three set points, but I managed to keep my head cool and just fight back,'' Wozniacki said.

In the early Red Group match, Wimbledon champion Petra Kvitova defeated Vera Zvonareva of Russia 6-2, 6-4.

Making her first appearance at the season-ending tournament for the top eight players , Kvitova let a 4-1 lead slip to 4-all in the second set but broke again before wrapping up the win.

The top two players in each group advance to the semifinals.

This is the first time the tournament is held in Istanbul, after being staged in Doha, Qatar, the last three years.

The surface is a little bit weird,'' Radwanska said.It's pretty slow. So you really have to be used to it. I just hope I can play better in the next match.''

Later, Maria Sharapova will play U.S. Open champion Sam Stosur.