Combo photo show Li Na of China celebrates victory over Venus Williams (R) during their women's singles quarterfinal tennis match at the Beijing 2008 Olympic Games, August 14, 2008. [Agencies]

To a noisy home crowd, Chinese player Li Na produced another upset by edging past American seventh seed Venus Williams in women's singles quarterfinals.

The former world top 20 player came into the Olympics unseeded and 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 a 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."