Kim Clijsters of Belgium reacts during her semi-final match against Serena Williams at the U.S. Open tennis tournament in New York September 12, 2009. Clijsters won the match 6-4 7-5, which ended in controversy when the American was called for a foot-fault on a second serve to go match point down. The Belgian, playing in only her third tournament after taking a two-year break to start a family, became the first mother to reach a grand slam final since Evonne Goolagong achieved the feat at Wimbledon in 1980. [Xinhua/Shen Hong]

Former World No. 1 Kim Clijsters reached the U.S. Open women's singles final at her first comeback grand slam on Saturday with a controversial straight sets win over Serena Williams.

Serena Williams (L) of the U.S. talks with tournament referee Brian Earley (C) and an official during her semi-final match against Kim Clijsters of Belgium at the U.S. Open tennis tournament in New York, September 12, 2009. Clijsters won the match 6-4 7-5, which ended in controversy when Williams was called for a foot-fault on a second serve to go match point down. [Xinhua/Shen Hong]

The Belgian beat the defending champion 6-4, 7-5 after a day-long rain delay to advance to the final just weeks after returning to the tour from a two-year break to start a family.

Trailing 5-6, 15-30 in the second set, Williams whacked her second serve but was called a foot-fault by the lineswoman and put at match point down.

Serena Williams of the U.S. reacts during her match against Kim Clijsters of Belgium at the U.S. Open tennis tournament in New York, September 12, 2009.[Xinhua/Reuters Photo]

The fierced Williams was then seen roar at the lineswoman and given a point penalty to lose the match.

The other semifinal of the women's singles sent in teenage Dane Caroline Wozniacki, who defeated unseeded and error-prone Belgian Yanina Wickmayer 6-3, 6-3.

Later on Saturday, the women's doubles semifinal between third seeds Samantha Stosur/Rennae Stubbs of Austria and top seeded Cara Black of Zimbabwe and Liezel Huber of the United States was suspended while the former duo led 7-5.

On the men's part, third seed Rafael Nadal needed just 34 minutes to complete a postponed 7-6, 7-6, 6-0 victory over Chile's Fernando Gonzalez.

Nadal will face sixth seed Argentine Juan Martin del Potro in Sunday's men's semifinals, while five times champion Roger Federer faces fourth-seeded Serb Novak Djokovic on the same day.