French Open champion Jelena Ostapenko is out of the US Open, losing in the third round 6-3 6-2 to Russian Daria Kasaktina after hitting 38 unforced errors.

The Latvian 12th seed, who blasted her way to the Roland Garros title in June, got off to a fast start but the unseeded Kasaktina mixed her game with sliced backhands and chopped forehands to slow her opponent down.

The plan worked as after winning the first three games, Ostapenko grew frustrated and exited after she netted a backhand on the second match point at the end of a lung-busting rally.

Ostapenko complained of nausea and illness during the match.

“In the beginning I was a little bit nervous but I tried to stay focused and play my game and it paid off,” said Kasaktina, who faces Estonian qualifier Kaia Kanepi for a place in the quarter-finals.

Karolina Pliskova showed the steel of a world No.1 as she fought off a match point to claim a riveting 3-6 7-5 6-4 comeback win over Zhang Shuai.

Pliskova, runner-up at Flushing Meadows last year, would have lost her world number one ranking had she been beaten on Arthur Ashe Stadium but instead moved another step closer to a first career grand slam title.

“Last grand slam of the season and knowing you played fine last year, you just want to play that good again,” Pliskova said.

“I don’t feel like I’m playing that good again, but I’m still in the draw, actually, so I’m not going to be that sad.”

American Shelby Rogers’ marathon run in New York has ended in the third round.

Rogers, two days after beating Australian Daria Gavrilova in the longest women’s singles match in US Open history, lost to No.4 seed Elina Svitolina 6-4 7-5.

On match point, Svitolina hit a thunderous forehand that hit the net cord and dribbled over for a winner.

On Thursday, Rogers outlasted Gavrilova 7-6 (8-6) 4-6 7-6 (7-5) in 3 hours, 33 minutes.

CoCo Vandeweghe is another local hope moving on to the round of 16, after she outlasted 10th-seeded Agnieszka Radwanska 7-5 4-6 5-3.