Stanford, California:Wimbledon champion Serena Williams has lost to Australia's Samantha Stosur, falling 6-2, 3-6, 6-2, in the quarterfinals of the Bank of the West Classic.
Stosur saved nine of 10 break points on Friday and played a steady game against the top-seeded Williams, who had a nine-match winning streak snapped.
Stosur is seeking her first WTA Tour title. She will play the winner of the quarterfinal between Jelena Jankovic and Marion Bartoli.
Third-seeded Elena Dementieva of Russia also advanced to the semifinals, beating Daniela Hantuchova of Slovakia 6-2, 6-4.
Dementieva will play the winner of the match between Maria Sharapova and Venus Williams.