FILE PHOTO: China's Wang Qiang. Photo: Eduardo Munoz Alvarez/AP

NEW YORK  China's Wang Qiang upset French Open champion Ash Barty 6-2, 6-4 on Sunday at the US Open to reach a first career grand slam quarter-final.

The 18th-seeded Wang prevailed on fourth match point against second seed Barty who won both of their previous meeting but failed to convert on all of her nine break points and piled up 39 unforced errors, to Qiang's 14.

"I was very focused, I tried to hit aggressive," said Wang who next meets six-time champion Serena Williams or Petra Martic but is not getting too wound up about her upcoming task.

"That's my coach's home work. My coach will tell me how to play next. I want to just enjoy it," she said.

Other action Sunday included former finalist Karolina Pliskova v Johanna Konta on the women's side, while men's fourth-round action included a duel between title holder Novak Djokovic and 2016 champion Stan Wawrinka, plus Roger Federer v David Goffin.