Australian Sam Stosur has been bundled out of the US Open in the second round by China's Zhang Shuai.

Zhang, Stosur's doubles partner at this year's Open, was in control from the outset, as she won 6-3, 6-3 to reach the third round at the US Open for the first time in her career.

Zhang, 27, said post match she was in shock at beating Stosur, who she values both as a competitor and a mentor.

on Day Four of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2016 in the Flushing neighborhood of the Queens borough of New York City.

“She helped me a lot, I'm feeling so sorry about her,” Zhang said.

“I still can't believe I beat Sam... I didn't think I can beat her because she was champion at the US Open because she has very good spin, very good serve. It's tough to play against her.”

Zhang now faces Kazakhstan's Yaroslava Shvedova in the third round.