Third seed Jessica Pegula and Wimbledon finalist Ons Jabeur suffered frustrating defeats in the fourth round at the US Open.

Despite her success on the WTA Tour, the 29-year-old has yet to go beyond the quarter-finals at any Grand Slam.

Last year’s runner-up Jabeur lost 6-2 6-4 to China’s Zheng Qinwen.

Qinwen will face either Aryna Sabalenka or Daria Kasatkina in the quarter-finals while Keys, runner-up in New York in 2017, will face Wimbledon champion Marketa Vondrousova.

Jabeur was left heartbroken after losing a second Wimbledon final in July and has struggled with illness during her time in New York.

She has also struggled for rhythm, having to come from behind to beat Marie Bouzkova in the third round.

She was broken twice in the first set against Qinwin, rescuing one of them before handing the momentum straight back to her opponent.

She saved four match points in the second as Qinwen’s nerves struck, but the Chinese 23rd seed held on to secure a place in the last eight of a major for the first time.

Off-colour Pegula stumbles at a Slam again

Keys and Pegula are good friends and the two shared a warm hug at the net following their fourth-round match, but Pegula could not hide her disappointment.

She had won the Canadian Open in the build-up to the final major of the year, registering a notable victory over top ranked Iga Swiatek in the process.

However, she has consistently struggled to break through at the majors, having never gone beyond the last eight in six attempts.

Pegula was off-colour from the start, struggling to find her rhythm against the big-hitting Keys.

She hit just three winners in the first set, which she lost in just 28 minutes, and quickly found herself a break down in the second.

Pegula was able to take advantage of a blip from 17th seed Keys to retrieve the break for 3-3, but she lost the next three games as Keys reasserted her dominance.

Vondrousova wins despite arm issue

Keys will now face Vondrousova, who had to fight back to see off spirited American Peyton Stearns 6-7 (3-7) 6-3 6-2.

Czech ninth seed Vondrousova, who has reached the quarter-finals in New York for the first time, appeared to be struggling with an arm injury during the match.

She took medication at the start of the second set for the issue and later said the heaviness of the tennis balls was impacting her..

“It’s just from the balls. They are very heavy and the season is long, so I feel like you just have to fight through it,” she said.

“I feel like the balls are not helping with everything. It’s tough but I just fought through it and I’m very happy with my win”.

The 24-year-old was upset later when she told doubles partner Barbora Strycova she would not be able to compete alongside her.

Fellow Czech Strycova is competing in her last tournament and the duo’s withdrawal from the doubles marks the end of the end of her career.

“Of course it was a bit sad, I cried a bit when I told Barbora [she couldn’t play doubles] but I had so many injuries that I don’t want to play with some more,” Vondrousova added.