Italy’s Flavia Pennetta has shocked two-time Wimbledon champion and Czech fifth seed Petra Kvitova 4-6 6-4 6-2 to reach her second US Open semi-final.

Pennetta, who ended Sam Stosur’s tournament in the fourth round, will face the winner of the clash between two-time Australian Open champion Victoria Azarenka and Romanian second seed Simona Halep for a place in Saturday’s final.

“I’m really happy right now,” Pennetta said.

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“I was just trying to fight every ball, running and push everything I can.

The Czech won the first set, but Pennetta fought back. Photo: Getty

“I didn’t think to get through this match. In the second set I was playing and playing, it was unbelievable.”

Kvitova looked well on her way to a first semi-final appearance when she easily took the opening but the veteran Pennetta kept her cool on another sizzling day in New York.

Serving at 5-4 in the second Pennetta wobbled, missing an easy winner to hand Kvitova a break chance but the Italian did not buckle and hung on to level the match and then dominated the third set as Kvitova wilted in the oppressive heat.

Kvitova was one of only two players to beat Serena Williams this season, had been in superb form winning her final US Open tuneup in New Haven and carried that momentum into Flushing Meadows, reaching the quarter-finals without dropping a set.

The Italian flag will feature prominently in the semi-finals with the 33-year-old Pennetta joined in the last four by 32-year-old compatriot Roberta Vinci, who booked her spot on Wednesday (AEST) with a victory over Frenchwoman Kristina Mladenovic.

Vinci will face world number one Serena Williams, who holds all four major titles and seeks a calendar Grand Slam, in the semi-final.

Williams is chasing the first calendar Grand Slam since Steffi Graf in 1988 and trying to match Graf’s Open Era career record of 22 Slam singles titles, two shy of Margaret Court’s all-time record.