|Agnieszka Radwanska of Poland hits a return to Petra Kvitova of the Czech Republic during the first round of WTA Championships 2012 in Istanbul of Turkey on Oct. 23, 2012. Agnieszka Radwanska won the macth 2-0. (Xinhua/Ma Yan)
ISTANBUL, Oct. 23 (Xinhua) -- Poland's Agnieszka Radwanska defeated reigning champion Petra Kvitova of the Czech Republic, 6-3, 6-2 Tuesday as the 2012 WTA Championships kicked off in Turkish biggest city Istanbul.
In another White Group match, former world No. 1 Maria Sharapova of Russia, seeded number two, beat seventh-seed Sara Errani 6-3, 6-2. The Russian Sharapova also beat the Italian Errani in this year's French Open final.
Third-seed Serena Williams took care of fifth-seeded German left-hander Angelique Kerber 6-4, 6-1 in the Red Group.
The single round robin will continue to 26th and the top two players in each group will advance to the semifinals, and the winners will square off in the final on Sunday.
The winner of this 4.9 million U.S. dollars event could collect as much as 1.75 million dollars for the championship prize.