Mauresmo, the top seed and a two-time defending champion at the event, beat Frenchwoman Virginie Razzano, 7-6 (8-6), 7-5. Petrova, the No. 3 seed, topped fellow Russian Vera Zvonareva, 7-6 (7-2), 6-4.
Fourth-seeded Russian Elena Dementieva had to retire from her second-round match against countrywoman Elena Likhovtseva, who was leading 6-2, 1-1. Dementieva called it quits because of a rib injury.
In Friday's quarterfinals, Petrova meets No. 7 Anna Chakvetadze; Mauresmo faces sixth-seeded Dinara Safina of Russia; Elena Likhovtseva meets France's Tatiana Golovin; and Ivanovic will play second-seeded Belgian Kim Clijsters.