Petra Kvitova has revealed her frustration with her serving display after losing to Flavia Pennetta in the US Open quarter-finals.

The fifth seed looked to be on course for the last four before Pennetta bounced back from disappointment in the first set to win 4-6 6-4 6-2, and Kvitova was left in no doubt which area of her game had the biggest impact.

"I think I should a little bit serve better, but on the other side, I think that she returned very well. I made a lot of double faults today, and it was just presents to give her," the two-time Wimbledon champion, who delivered nine double faults, told the US Open website.

"On the other side, I mean, if I am not really counting the serves sometimes, I left everything what I could today, as I said already, and she didn't miss at all. She was very consistent player. She moves very well, and it was tough to have any winners and everything."

Pennetta will take on second seed Simona Halep in the semi-finals.