Simona Halep says she has no pressure to perform at the US Open, despite her lofty standing in the women's game.

World number two Halep battled injury and fatigue to beat 24th seed Sabine Lisicki 6-7 (6-8) 7-5 6-2 in the fourth round at Flushing Meadows on Monday.

Halep has enjoyed a successful year on tour after winning in Shenzhen, Dubai and Indian Wells, while the Romanian star reached finals at the Canadian Open and Western and Southern Open leading into New York.

However, the 2014 French Open finalist is not feeling the heat as she prepares to meet former number one and two-time grand slam champion Victoria Azarenka in her maiden US Open quarter-final.

"I had many expectations in French Open and Wimbledon and wasn't good. So here I changed a little bit my mind, and I have no expectations," said Halep, who is 44-11 on tour this year.

"Azarenka is playing well, started to play well again. She has experience already. She won two grand slams. So will be a tough one. But I know that I have my chances."

Halep added: "I have no pressure. Actually, I feel it. But I play well when I have pressure. 

"I don't care about the result. I just want to go there and to try to do everything I can in that day."

Halep was forced to dig deep on Louis Armstrong Stadium after needing heavy strapping to her left leg.

The grand slam hopeful required medical attention throughout the three-set battle due to her troublesome thigh, but the 23-year-old hopes to make a swift recovery in time for the last eight.

"Today was really tough against Lisicki because she was hitting strong. I had just to stay there, to run a lot," said Halep. "I did a step behind the baseline and wasn't good. I had to run a lot. That's why I felt my muscle. 

"But at the beginning of the tournament, I was perfect. I was ready to start it.

"I feel it. I feel pain. But tomorrow I have day off so I have time to recover. I hope just to be okay to play another match."