Petra Kvitova of the Czech Republic reacts to lost point against Venus Williams of the United States during US Open quarterfinals in New York, US, Sept 5, 2017. [Photo/Agencies]

Earlier, second seed Karolina Pliskova appeared to suffer no ill-effects of playing without a coach when the tall Czech swept aside Magda Linette 6-2 6-1 to also reach the last eight.

The world number four, who split with coach David Kotyza last week, capitalized on an early break to win the first set in little more than half an hour.

Pliskova's power proved too much for Linette, who was broken in the second game of the second set, before the Pole's wayward forehand helped her opponent book a place in the next round.

"I felt great today on the court," Pliskova said. "I think my serve was working well... I'm really happy with my win today."

She now faces seventh-seeded German Angelique Kerber who overcame Russian Daria Kasatkina 7-6(5) 6-3.

Another Russian Anastasia Pavlyuchenkova labored to a 6-4 4-6 6-2 win over China's Wang Qiang, who inflicted a 'double bagel' on eighth seed Kristina Mladenovic in the first round.

Reuters