Defending champion Kim Clijsters rallied for a three-set victory over Jelena Jankovic to reach the quarter-finals of this 600,000-dollar WTA Tour hardcourt tournament.
The top-seeded Belgian, seeking her fourth Stanford title in six years, got off to a rocky start but steadied to post a 5-7 6-2 6-2 victory over the unseeded Serbian.
Clijsters, one of four players with a first-round bye, will next face the winner of Thursday's second-round clash between Russian Vera Zvonareva and France's Nathalie Dechy.
She is trying to add another title to those she won here in 2001, 2003 and 2005 - the last coming after she missed the 2004 edition with a wrist injury.
In other second-round action on Wednesday, France's Tatiana Golovin upset sixth-seeded Ai Sugiyama of Japan 6-2 6-3.
Australian Samantha Stosur also posted an upset, ousting seventh-seeded Shahar Peer of Israel 7-5 6-3.
American Jill Craybas advanced to the quarters, beating her US Fed Cup teammate Shenay Perry 6-3 3-6 7-6 (7/2).
There also were three first-round matches played on Wednesday.
Zvonareva, who claimed her second title since June at Cincinnati on Sunday, knocked off eighth-seeded Slovenian Katarina Srebotnik - the same woman she beat in the Cincinnati final - 6-4, 6-3.
She next will face Dechy, who beat Italian Maria Elena Camerin 0-6 7-6 (8/6) 6-3.
Japan's Akiko Morigami booked a second-round match against second-seeded Patty Schnyder of Switzerland with a 6-0 6-3 triumph over Gisela Dulko of Argentina.