Simona Halep was grabbing her left thigh and arching her aching back, not to mention doing some heavy breathing at the end of long rallies against Sabine Lisicki.

It's the end of the Grand Slam season at the U.S. Open and players come to the tournament in various states of physical distress, then have to play in the heat and humidity on the hard courts of the National Tennis Center. It's Survival, Flushing Meadows.

On Monday, Halep survived. The Open's No. 2 seed pulled out a 6-7 (6) 7-5, 6-2 win over Lisicki to reach the quarterfinals and a matchup with Victoria Azarenka.

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After losing the tiebreak, in which she was a point from taking the first set, Halep called for the trainer and took a medical timeout to get her left thigh wrapped. But she still found it painful and grimaced often when having to stop hard on the left leg to hit a backhand. She toughed out the second set after being broken while serving for it. The players then were allowed a 10-minute break under the heat rule, and Lisicki also called a medical timeout during it, her left knee giving her fits. When play resumed, Lisicki developed cramping in her left leg.

"At the beginning . . . I was cramping in my back. Then the leg was worse,'' Halep said. "It's tough to play in the U.S. Open because it's the last one. All of us are playing like crazy all year, many tournaments.''

Azarenka continued her strong run with a 6-3, 6-4 win over Varvara Lepchenko, building on her impressive three-set victory over Angelique Kerber in the third round. Azarenka, the two-time U.S. Open runner-up to Serena Williams, came to this Open having played only 12 events this year, and this summer was hindered by a left thigh injury.

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Things are looking up for her in Flushing Meadows.

"I think it is all coming from probably March in a progression slowly, improving every match to match,'' she said. "I could see the improvement already I have done from Toronto to here. So I think it's just on a roll of progression.''

In March, she hired coach Sascha Bajin, who once worked with Serena Williams.


"What Sascha brought is a lot of great, positive energy, a lot of motivation,'' Azarenka said. "He's the type of guy who pushes you in practice. I felt that I have been missing that a little bit of an extra . . . He just grinds and pushes me, frustrates me sometimes during practice.''

Flavia Pennetta, the 33-year-old Italian, got into the quarterfinals with a 6-4, 6-4 win over 2011 champion Samantha Stosur. Pennetta's best results in a Grand Slam by far have come at the Open. This is the fifth time she has made the quarterfinals, and she reached the semis in 2013.

Pennetta will play Petra Kvitova in the quarterfinals. Kvitova beat British qualifier Johanna Konta, 7-5, 6-3, in the first match on Ashe Monday night.