Second-seeded Paula Badosa survived a scare on the way to a 6-2, 5-7, 7-6 (7/5) victory over US qualifier Elizabeth Mandlik on Wednesday in the WTA hardcourt tournament in San Jose, California.
Badosa will next face the winner of Thursday night's marquee clash between four-time Grand Slam champion Naomi Osaka and sixth-seeded American Coco Gauff.
Japanese superstar Osaka is unseeded as she plays her first tournament since falling in the first round of the French Open, where she was battling a left Achilles tendon injury.
Gauff, the French Open runner-up, is seeded sixth.
Third-seeded Tunisian star Ons Jabeur, playing her first match since her historic runner-up finish at Wimbledon, pulled away late to beat American Madison Keys 7-5, 6-1.