Star Metro - Three matches to watch on Sunday at the US Open

Australia's Alexi Popyrin, who stunned defending champion Djokovic in the third round to quash the Serb's latest bid for a 25th Grand Slam title will face another tough match against American crowd-pleaser Frances Tiafoe for a place in the quarter-finals.

Women's fourth-round action includes a pair of intriguing rematches. Defending champion Coco Gauff will try to avenge a Wimbledon fourth-round loss to fellow American Emma Navarro while China's Olympic gold medallist Zheng Qinwen faces Donna Vekic of Croatia in a rematch of the Paris Games final.

Second-ranked Australian Open winner Aryna Sabalenka is also in action as she tries to become the first woman since Angelique Kerber in 2016 to win both hard court Grand Slam titles in the same year.

AFP Sport looks at three matches to watch on day seven of 2024's final Grand Slam, which will conclude on September 8 (x denotes seeded player):

Frances Tiafoe (USA x20) v Alexei Popyrin (AUS x28)

Tiafoe electrified the Arthur Ashe Stadium crowd with a five-set triumph over fellow American Ben Shelton. Now he'll take on giant-killer Popyrin, who brought down Djokovic in his first appearance on the cavernous main court of the Billie Jean National Tennis Center.

Friends off court, the two have never played, but Tiafoe expects it to be a barn-burner against the Aussie who earned his first ATP Masters 1000 title in Montreal this month.

"I'm probably playing the best tennis of my life right now," Tiafoe said. "He's always been really talented. He's starting to put it together.

"You don't expect anything easy at this point."

Popyrin said he would need to get his big serve in high gear to counter Tiafoe's aggression at the net.

"It will be interesting to play against him," the 25-year-old Sydneysider said. "We have practiced a bunch of times."

Emma Navarro (USA x13) v Coco Gauff (USA x3)

Gauff has endured an uneven season since bagging her maiden major at the US Open last year, and a fouth-round loss to Navarro at Wimbledon was just one of the unwelcome surprises.

"That match at Wimbledon, I think I mentally just literally collapsed on the court," Gauff recalled. "I was very frustrated and she played well.

"I think going into this match, I just need to know that I need to bring it and mentally be there from the beginning to the end because she's going to be a tough opponent."

For her part Navarro was looking forward to an all-American US Open clash on the imposing Ashe Stadium -- a court whose sheer size she said made her dizzy when she practiced on it as a junior.

"That's kind of an experience that is something I could have never even have dreamed of," she said. "I'm playing the defending champ."

Zheng Qinwen (CHN x 7) v Donna Vekic (CRO x24)

Vekic says Zheng was just "too good" in the Olympic final on the red clay of Roland Garros, but she's hoping the change to the hard courts of Flushing Meadows will work in her favor just weeks after she settled for silver at the Paris Games.

"It's a new match. It's a different surface, thankfully for me," said Vekic, a four-time WTA champion who reached the US Open quarter-finals in 2019. "I'm going to try to prepare well and do a good tactic with my team, and hopefully it will be a different outcome."

But Zheng, China's first tennis singles gold medallist, has solid hard court credentials, including a runner-up finish at the Australian Open this year.

But the world number seven, itching to join trailblazing compatriot Li Na as a Grand Slam winner, said Wimbledon semi-finalist Vekic would be a tough challenge.

"I have to be ready, play 100 percent," Zheng said.

T.Murray--SMC