Former world  No. 1 women's tennis player Serena Williams of the United States has upset Russian fifth-seed Nadia Petrova in third round action at the Australian Open in Melbourne.

Williams battled back from a first-set trouncing to advance to the fourth round in three sets, 1-6, 7-5, 6-3. The seven-time Grand Slam champion is unseeded following an injury-plagued season last year. She won the Australian Open in 2003 and 2005.

Defending women's champion and second-seed Amelie Mauresmo of France cruised past unseeded Czech player Eva Birnerova in straight sets, 6-3, 6-1. Third-seed Svetlana Kuznetsova scored a 6-1, 6-4 victory over fellow-Russian Maria Kirilenko.

Men's No. 1 and defending champion Roger Federer of Switzerland breezed into the fourth round with a straight sets victory over Russian Mikhail Youzhny, 6-3, 6-3, 7-6.

American Andy Roddick, the sixth seed, won a close four-sets match over 2005 Australian champion Marat Safin of Russia, 7-6, 2-6, 6-4, 7-6.

Seventh-seed Tommy Robredo of Spain ousted American Sam Querrey in four sets (6-4, 6-7, 6-2, 6-1), while Croatian Mario Ancic, the ninth seed, eased past Dominik Hrbaty of Slovakia (6-3, 6-2, 6-1).

Other seeded women advancing were (7) Elena Dementieva of Russia, (10) Nicole Vaidisova of the Czech Republic, (11) Serbian Jelena Jankovic and (16) Israel's Shahar Peer.

Some information for this report was provided by AFP, AP.