Petrova, ranked 10th in the world, outlasted Alona Bondarenko 4-6, 6-3, 7-6 (7-5). Petrova had seven aces, but also committed 11 double faults in a match that lasted 2 hours, 36 minutes.
Petrova will face fifth-seeded Aleksandra Wozniak Saturday. Wozniak fought off Tamira Paszek 6-3, 3-6, 7-6 (9-6).
The other semifinal will send Carolina Wozniacki against Elena Vesnina.
Wozniacki coasted past Daniela Hantuchova 6-2, 6-2 and Vesnina survived against Dominika Cibulkova 7-5, 6-7 (5-7), 6-3.
Copyright 2009 by United Press International.