NEW YORK - French Open champion Li Na was upset 6-2 5-7 7-6 by Czech qualifier Petra Cetkovska in the semi-finals of the New Haven Open on Friday.

Li Na of China hits a return to Samantha Stosur of Australia during their third round match of the Cincinnati Open tennis tournament in Cincinnati, Ohio, Aug 18, 2011. [Photo/Agencies]

Cetkovska, ranked a career-high 40th in the world, will face world number one Caroline Wozniacki in Saturday's final, the Dane having beaten Italy's Francesca Schiavone 7-6 6-3 in the last four.

Cetkovska clinched the decisive tiebreak 11-9 at the end of a battle with Li lasting two hours and 41 minutes.

The 26-year-old Czech has yet to win a WTA event but is on an upward curve, reaching the fourth round at Wimbledon this year after winning three ITF titles last season.

Caroline Wozniacki of Denmark serves to Christina McHale of the US during their second round match of the Cincinnati Open tennis tournament in Cincinnati, Ohio, Aug 17, 2011. [Photo/Agencies]

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Wozniacki wins US Open tune-up at New Haven

World number one Caroline Wozniacki shrugged off the distraction of a long rain delay and the threat of Hurricane Irene to win the New Haven WTA title for the fourth year in succession on Saturday.

The top-seeded Dane defeated Czech qualifier Petra Cetkovska 6-4 6-1 to boost her confidence ahead of the US Open which starts on Monday.

The final was moved forward by four hours to avoid the expected arrival of Hurricane Irene and then interrupted by more than an hour and a half because of rain after the first set.

Wozniacki, 21, has now won 18 WTA titles including six this year but has yet to lift a grand slam crown although she was a finalist at the US Open two years ago.