No. 5 seed Ana Ivanovic won her first-round match in the Bank of the West Classic, defeating Sabine Lisicki 7-6 (2), 6-1 on Tuesday.
The former world No. 1 lost to Lisicki in three sets in their previous meeting at Wimbledon.
Ivanovic has won three WTA Tour titles this season after failing to win a tournament in 2013. She owns 14 career titles.
The Serbian next faces qualifier Carol Zhao, a sophomore at Stanford who was leading Yanina Wickmayer 6-2, 1-0 when the Belgian retired because of a viral infection.
In other matches, Monica Puig beat seventh-seeded Carla Suarez Navarro, 6-3, 7-5, and Garbine Muguruza eliminated defending tournament champion Dominika Cibulkova, 6-2, 4-6, 6-2.