Vera Zvonareva won her first match since finishing as Wimbledon runner-up in the first round of the Mercury Insurance Open, but former world number one Ana Ivanovic was beaten in San Diego.
Zvonareva, who lost her first grand slam final to Serena Williams at Wimbledon, claimed a 6-0 3-6 6-4 win over Slovakian wild card Dominika Cibulkova.
“It was a tough one,” said the third-seeded Russian.
“I started really well, but she’s a great fighter and started playing more aggressively. I was up and down a little bit and she was able to relax and come back. That third set was a great fight.”
Ivanovic, who won the 2008 French Open and was playing as a wild card, was beaten 7-6 (7/5) 6-3 by Israeli seventh seed Shahar Peer. It was the third time Peer has beaten Ivanovic as she continued her 100% record against the Serbian.
Agnieszka Radwanska and Flavia Pennetta also progressed. Fourth seed Radwanska beat qualifier Chanelle Scheepers 7-5 6-3 and Pennetta, the fifth seed, beat Kateryna Bondarenko 6-2 7-5.
Elsewhere, Daniela Hantuchova battled from a set down to defeat Marion Bartoli 3-6 7-6 (7/3) 6-4, while Melanie Oudin overcame fellow American Jamie Hampton 6-3 6-4.
Svetlana Kuznetsova defeated eighth seed Yanina Wickmayer 6-3 2-6 6-1, Zheng Jie claimed a 6-3 6-2 win over qualifier Shenay Perry and Maria Kirilenko beat another qualifier, with a 6-4 6-7 (4/7) 6-3 win over Kurumi Nara.
Yaroslava Shvedova defeated Nadia Petrova 5-7 6-4 6-1 but Gisela Dulko’s challenge ended prematurely as she was forced to retire with a sprained right ankle while trailing qualifier Coco Vandeweghe 6-0 3-0.