Defending champion Coco Gauff says she needs to maintain her focus throughout her US Open fourth-round tie against Emma Navarro on Sunday after mentally 'collapsing' during her shock defeat by her at Wimbledon.

Third seed Gauff was upset by Navarro in the last 16 at the All England Club in July, losing in straight sets.

The pair meet in an all-American tie second on Arthur Ashe Stadium.

"I feel like that match at Wimbledon I think I mentally just literally collapsed on the court. I was very frustrated, and she played well," Gauff said.

"I have to expect her to play her best tennis and I just need to know that I need to bring it and mentally be there from the beginning to the end."

Gauff, 20, is bidding to become the first woman to defend her US Open title since Serena Williams in 2014, while 23-year-old Navarro - the 13th seed - will be hoping to reach the quarter-finals at Flushing Meadows for the first time.

Elsewhere, Chinese seventh seed Zheng Qinwen plays Croatian 24th seed Donna Vekic in a rematch of the Paris Olympics women's singles final.

Zheng beat Vekic 6-2 6-3 in August to win gold and has followed that up in New York with her best ever run at a Grand Slam.

Second seed Aryna Sabalenka is also back in action, with the Belarusian playing Belgian 33rd seed Elise Mertens.

On the men's side of the draw, Russian sixth seed Andrey Rublev opens the action on Arthur Ashe Stadium from 17:00 BST against Bulgarian ninth seed Grigor Dimitrov.

Australian 28th seed Alexei Popyrin's reward for beating 24-time Grand Slam champion Novak Djokovic is a tie with American 20th seed Frances Tiafoe, while German fourth seed Alexander Zverev faces another American in Brandon Nakashima.