Persistent rain played havoc with the fourth day's play, allowing barely 90 minutes play throughout the day, with the last 16 players fighting it out to reach the quarter-finals.

Petrova put out fellow Russian and tenth-seed Elena Dementieva with a 6-3, 6-3 win, the seventh seed rarely tested by her compatriot.

Earlier in the day, Serbian Ana Ivanovic became the first to reach the last eight after her opponent Ukrainian Alona Bondarenko retired in the second set with an ankle injury when she was 5-0 down having lost the first set 6-3.

Germany's final survivor Martina Mueller, who knocked out the 13th seed Shahar Peer to reach the last 16, was comfortably beaten 6-3, 6-2 by third-seeded Russian Svetlana Kuznetsova.

World number-one Justine Henin was scheduled to face Italian Maria Elena Camerin on Thursday, while second-seed Amelie Mauresmo was also set to take on Ukrainian Julia Vakulenko in the other key matches.