Li Na of China celebrates after defeating Venus Williams of the Unied States during the women's singles quarterfinal of the Beijing 2008 Olympic Games tennis event at the Beijing Olympic Green Tennis Court in Beijing, China, Aug. 14, 2008. Li Na won the match 2-0. (Xinhua/Wang Yuguo) Photo Gallery>>>

    BEIJING, Aug. 14 (Xinhua) -- Chinese player Li Na continued her top form in the Olympic Games tennis event as she upset American seventh seed Venus Williams in the quarterfinals of the women's singles on Thursday.

    Li, a former world top 20 player who came into the Olympics unseeded, had beaten Russian third seed Svetlana Kuznetsova in the first round of the event.

    Li pulled back from 4-1 down to steal the first set 7-5 from the Sydney 2000 gold medalist, who served nine double faults in the opening set and was kept guessing by Li's variety of shots.

    Li retained her momentum in the second set, going 3-1 up and breaking again in the 11th game to sneak ahead 6-5. On Li's second match point, Williams put a forehand service return into the net.

    "It's still overwhelming. I can't believe I made it. It gave me more confidence to go further," said Li, who will in the semifinals play the winner of the match between sixth seed Dinara Safina and second seed Jelena Jankovic.

    "Everyone knows she is good player, the best in the world, and she won Wimbledon this year. At the beginning of the match she had a huge, big serve and I could not pick the ball, but I managed to tell myself play the ball back and try my best."

    In an early match, Serena Williams, Venus' younger sister, was also knocked out from the quarterfinals after losing to Russian fifth seed Elena Dementieva.

    This marks the second time this year that both Williams sisters fell in the same round on the same day at a big tournament. The two went out in the third round at the French Open.