The three-time former champion beat former world No. 1 Ana Ivanovic of Serbia, 6-3, 6-4, Monday to reach the quarterfinal round. Williams, who has not lost a single set during the tournament, will next take on Anastasia Pavlyuchenkova, the 17th seed from Russia.
The ladies top seed, Caroline Wozniacki, needed three sets Monday evening to defeat Svetlana Kuznetsova, 6-7, 7-5, 6-1, and advance into the quarterfinals. The world's No. 1 player on the women's side, Wozniacki rallied from one set down and losing 1-4 in the second set to beat the 15th-seeded Kuznetsova.
On the men's side Monday, American Mardy Fish lost a grueling match against Jo-Wilfried Tsonga of France, 6-4, 6-7, 3-6, 6-4, 6-2. The 11th-seeded Tsonga now faces former Open champion Roger Federer, who dispatched Juan Monaco in straight sets.