World No.24 CoCo Vandeweghe is loving life with new tennis coach Pat Cash and the results are showing on the court.

The American went through to Friday’s quarter-finals of the Stanford Classic after dispatching compatriot Nicole Gibbs 6-0 6-2.

“I think we’re out of the honeymoon,” she joked, before explaining the former Wimbledon champion is a hard task-master.

Vandeweghe will join the other top seeds in the last eight after all advanced in straight sets.

Second seed Petra Kvitova barely raised a sweat in her 6-2 6-2 demolition of Kateryna Bondarenko 6-2 6-2 in under an hour.

The two-time Wimbledon champion looked back to her best following a career-threatening knife attack at the end of last year. She did not face a single break point against her 111th-ranked Ukrainian opponent.

“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 the 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.

Next up for Kvitova is a quarter-final against eighth seeded American Catherine Bellis, who advanced with 7-6 (7-3) 6-2 victory over Veronica Cepede Royg of Paraguay.

Also through is Russian fourth seed Anastasia Pavlyuchenkova who beat American Alison Riske 6-4 6-0.