Flavia Pennetta overcame a 0-5 deficit in the tiebreaker of second second to beat 13th-seeded Chinese Peng Shuai, reaching the last eight of US Open on Sunday.

The 29-year-old Italian played a couple of her best career matches at Flushing Meadow, eliminating third seed Maria Sharapova in three sets of the third round before meeting Peng.

Pennetta seemed to be over consumed in the second set under the scorching sun and vomited a couple of time, but she held on to win in straight sets of 6-4, 7-6 (6) in two hours and 31 minutes.

"I was feeling really bad. I think it's because it's really humid today. It's hot. And also, when you are there you have a lot of emotion in the court. My body just need to breathe and I starting maybe to have the sensation to throw up," said Pennetta.

Peng, 25, bruised her right toe half way and had to call for medical treatment in the second set.

A nagging left hip injury also hampered her from giving her best, especially in serves.

"I can not find my power in serving for the hip hurting," said Peng, in explaining an average of 89 miles in first serve.

Peng was under par in grasping opportunities by converting only five of the 16 break points she earned, which just cost her chance of advancing.

Pennetta played more aggressively, nailing 41 winners, and executed her strategy, which she revealed after the third round victory over Sharapova, well of keeping Peng moving a lot.

Pennetta won her last WTA event held in Los Angeles in 2009 and shortly after she became the first Italian woman ever ranked in the top 10.

Her two US Open quarterfinals are her best Grand Slam-level finishes.

"This one is one of the worst I never feel in the court," said Pennetta.

Pennetta will next play against Angelique Kerker as the German cruised past Romanian Monica Niculescu 6-4, 6-3 in 93 minutes.

Peng had reached last 16 in all three majors this year except for the French Open, in which the Chinese was snapped in the last 32.