The Tunisian fifth seed has struggled to produce her best form since arriving in New York, having been laid low by illness which struck on the eve of the tournament.

After finding it difficult to breathe during her opening round victory on Tuesday, Jabeur once again found the going tough on Thursday, labouring to a 7-6 (9/7), 4-6, 6-3 victory over Czech teenager Linda Noskova.

Jabeur, chasing a maiden Grand Slam after losing back-to-back Wimbledon finals last year and this season, as well as finishing as a runner-up at last year's US Open, revealed after her win that she has been ill for most of the past week.

"I've been sick since I think Thursday," she said. "I'm taking a lot of medicine. I'm doing everything I can with my team trying to recover.

"Honestly, they have amazing doctors here, so they've been helping me. Every day I'm there. Basically took every medication they have.

"We try to manage what my health is right now. I'm glad it was two matches, two tests for me. I was trying to push myself to see what I can do, getting out of the comfort zone kind of.

"Hopefully will continue in a better shape and feel better for the next match."

Jabeur said she had been refreshed by a well-deserved holiday after Wimbledon, but admitted: "I'm a zombie because I have a flu.

"I took vacation after Wimbledon. I think that really helped me kind of take a second breath for the rest of the season.

"Emotionally could be tired, but I know if I just let go, I will regret it, so I want to continue and stay in New York as long as I can."

Jabeur will play another Czech in the third round on Saturday, Marie Bouzkova.

"I have a lot of respect for Czech tennis school, in general," Jabeur said. "They really, really have amazing players.

"Another test against Marie. It's going to be tough playing her, but I'm going to get ready and hopefully prepare well for the match."