Karolina Pliskova crushes Jennifer Brady to race into last eight

World number 91 Brady was overwhelmed on a sunny Arthur Ashe as last year's finalist Pliskova finally found her form after saving a match point in her three-set win over 27th seed Zhang Shuai in the third round.

It was a different matter in the morning New York sunshine on Monday as qualifier Brady was left utterly demoralised by the class, movement and shot selection of the Czech player, who must reach the final to hang on to her position as the game's top seed.

Pliskova will next face compatriot Lucie Safarova or another American player in CoCo Vandeweghe in the quarter-finals.

Brady struggled mightily with her service game, where she was only able to connect on 39 percent of her first serves compared to Pliskova's 67 percent.

Brady also struggled to read Pliskova's powerful serve and failed to convert either of her two break point chances.

"I think she was a little bit nervous," Pliskova said of the 22-year-old Brady during an on-court interview following the match.

"It was her first time on Ashe so I tried to take advantage of that."

Pliskova admitted she has been struggling with the pressure of having the number one next to her name but she got off to a good start here and played freely.

By the time the pair shook hands, Pliskova had thumped 23 winners, won 92 per cent of points on her first serve and made just nine unforced errors.

With Wimbledon champion Garbine Muguruza knocked out on Sunday night by Petra Kvitova, this now appears a golden chance for Pliskova to win her maiden grand slam title.