(CNN) -- Petra Kvitova dumped Caroline Wozniacki out of the WTA Championships with a straight sets victory that sealed her place in the final four. Kvitova, the 2011 Wimbledon champion, inflicted Wozniacki's second defeat in Istanbul, winning 6-4 6-2 to go top of the Red Group. World number one Wozniacki, who called the trainer on during her match after complaining of feeling sick, is rock bottom of the group after playing all three of her round robin games. After her victory Kvitova told CNN she was delighted to make the final four: "It's nice when I win and I'm happy to be in the semi-final. Istanbul is a great place and it is great experience for me.
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Petra Kvitova beats Caroline Wozniacki to make semis at WTA Championships
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Kvitova wins 6-4 6-2 to knock world No.1 Woznaicki out of tournament
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Victoria Azarenka joins Kvitova in the final four after beating China's Li Na
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Agnieszka Radwanska beats Vera Zvonareva to keep hopes of semi berth alive
@placeholder told the WTA's official web site: "Li Na has such a good return and likes to dominate from the beginning, so I tried to serve well and take that away from her.