"I served very well, and I was just trying to play my game, which I always try, and sometimes that works, sometimes not," Kvitova, who hit 31 winners, said after her victory in California.
Kvitova is playing her fourth event since spending six months recovering from stab wounds to her left hand inflicted by an intruder at her home in the Czech Republic.
The Czech suffered second round losses at the French Open and Wimbledon but now has the U.S. Open, starting later this month, firmly in her sights.
Next up for Kvitova is a quarter-final against eighth seeded American Catherine Bellis, who advanced with 7-6(3) 6-2 victory over Veronica Cepede Royg of Paraguay.
All four second-round matches on Thursday were won in straight sets as the form book prevailed.
Russian fourth seed Anastasia Pavlyuchenkova beat American Alison Riske 6-4 6-0, while sixth seed CoCo Vandeweghe thrashed
fellow American Nicole Gibbs 6-0 6-2.
Vandeweghe seems to be thriving under the guidance of coach Pat Cash.
"I think we're out of the honeymoon," she joked, before explaining that Cash in a hard task-master.
All eight seeds are through to Friday's quarter-finals with top seeded Wimbledon champion Garbine Muguruza opening proceedings against Ana Konjuh of Croatia.
(Reporting by Andrew Both in Cary, North Carolina; Editing by John O'Brien)
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