ISTANBUL — Petra Kvitova reached the semifinals of the WTA Championships on Thursday, dominating Caroline Wozniacki in a 6-4, 6-2 win that handed the top-ranked Dane her second loss at the season-ending tournament.

ISTANBUL — Petra Kvitova reached the semifinals of the WTA Championships on Thursday, dominating Caroline Wozniacki in a 6-4, 6-2 win that handed the top-ranked Dane her second loss at the season-ending tournament.

Kvitova joined Victoria Azarenka in the final four, with the Belarusian having earned a comfortable 6-2, 6-2 win over Li Na in the early match. In the day's late match, Poland's Agnieszka Radwanska beat sixth-seeded Vera Zvonareva 1-6, 6-2, 7-5.

Kvitova earned an early break in the first set and never looked troubled the rest of the way, hitting 36 winners compared to just six for Wozniacki. The Dane never earned a break point, and said she was feeling ill and tired playing her third match in three days.

"I have been feeling tired, and to get a little bit sick now, that's not the best if you want to beat the top players," Wozniacki said. "Today, Petra played well. And of course I wish I could have been 110 percent, but my body just didn't want the things that I wanted today."

Kvitova, this year's Wimbledon champion, broke two more times in the second set before clinching the victory with a backhand winner.

The Czech player improved her record to 2-0 in the round-robin phase, while Wozniacki fell to 1-2 after also losing to Zvonareva on Wednesday. Wozniacki still wrapped up the year-end No. 1 ranking after Maria Sharapova withdrew from the tournament with an ankle injury following her second loss on Wednesday.