NEW YORKCaroline Wozniacki became the highest seed to fall in the upset-filled women's draw at the US Open when Czech Petra Cetkovska stunned the Dane 6-4 5-7 7-6(1) at Flushing Meadows on Thursday.

The upset left only three of the top 10 seeds still alive in the year's final grand slam - number one Serena Williams, who is seeking the fourth women's calendar-year Grand Slam, second seed Simona Halep and fifth seed Petra Kvitova.

Cetkovska, who has tumbled to a 149th ranking after missing seven months with a hip injury before returning in March, was playing in the Open thanks to a special injury exemption.

She rode a powerful forehand that produced 29 of her 61 winners to victory over Wozniacki, saving four match points held by the Dane - all on winners off her racquet.

"I said it's now or never, so I just went for it," she said in an on-court interview with ESPN about saving the string of match points. "It's just amazing."

"So happy to be able to be back and to compete. It's amazing for me," said the 30-year-old Cetkovska who will play Italy's Flavia Pennetta, a straight sets winner over Romanian Monica Niculescu.

The Czech said the Arthur Ashe Stadium crowd helped lift her up. "The atmosphere, it's (like) nowhere else. It was just keeping me alive. I wanted to fight to the end," she said.