Eighth-seeded Elina Svitolina, who reached the quarterfinals of the French Open, needed three sets to beat qualifier Kateryna Bondarenko in the first round of the Bank of the West Classic on Tuesday.
The 20th-ranked Svitolina had lost four of her last five matches before knocking off her fellow Ukrainian in a match that lasted two hours, 31 minutes.
Svitolina plays favorite daughter Nicole Gibbs, a Stanford grad, in the second round.
In other matches, American Varvara Lepchenko topped Croatia's Mirjana Lucic-Baroni, 6-3, 2-6, 7-6(4); fellow Croatian Ana Konjuh downed China's Saisai Zheng, 6-3, 6-4; and Ajla Tomljanovic defeated Russian Vitalia Diatchenko, 3-6, 6-0, 6-0, and next meets seventh-seeded American Madison Keys.
World No. 1 Serena Williams pulled out of the event on Thursday due to an injury.