Czech star Petra Kvitova eased into the quarter-finals at the Bank of the West Classic, setting up a clash with CiCi Bellis.
Kvitova - the second seed - made light work of Kateryna Bondarenko in a 6-2 6-2 victory in Stanford on Thursday.
Playing at the WTA Tour tournament for the first time, two-time Wimbledon champion Kvitova needed only 60 minutes to race into the last eight thanks to 31 winners and just 10 unforced errors.
"I served very well, and I was just trying to play my game - which I always try, and sometimes that works, sometimes not," Kvitova said. "Kateryna is a dangerous player; she can catch lots of balls and I knew that I had to be focused and just play aggressive."
Kvitova and eighth-seeded American teenager Bellis will go head-to-head for a spot in the semi-finals.
Bellis, 18, overcame Paraguay's Veronica Cepede Royg 7-6 (7-3) 6-2.
Meanwhile, Anastasia Pavlyuchenkova beat Alison Riske 6-4 6-0 and Coco Vandeweghe eased past Nicole Gibbs 6-0 6-2.