Russia's Maria Sharapova continued her return from injury with a second-round win over third seed Victoria Azarenka at the Los Angeles Championships.
The former world number one, 22, who is returning from shoulder surgery, battled back from a set down to beat the Belarusian 6-7 (4-7) 6-4 6-2.
Current number one Dinara Safina eased into the third round with a 6-2 6-4 win over Slovakia's Daniela Hantuchova.
Sorana-Mihaela Cirstea beat fourth seed Caroline Wozniacki 1-6 6-4 7-6 (7-5).
Urszula Radwanska upset seventh seed Dominika Cibulkova 6-4 6-7 (6-8) 6-4.
Poland's Radwanska will play China's Li Na, who defeated Canada's Alexandra Wozniak 4-6 6-4 6-2.
Other winners included Russia's number five seed Nadia Petrova, who beat Israel's Shahar Peer 6-4 2-6 6-3, and Polish eighth seed Agnieszka Radwanska, who eliminated Japan's Ai Sugiyama 6-2 6-1.
Australia's Samantha Stosur set up a third-round meeting with Serbian eighth seed Ana Ivanovic by beating Russia's Maria Kirilenko 6-2 6-4.
