Kim Clijsters returns a shot to Caroline Wozniacki during the final at the U.S. Open in New York on Sunday. (Darron Cummings/Associated Press)

Kim Clijsters defeated Caroline Wozniacki 7-5, 6-3 to capture the U.S. Open women's title on Sunday.

Clijsters, playing in her third tournament and first Grand Slam in two years, became only the second mother to win the title. Evonne Goolagong Cawley of Australia did it in 1980.

"It was not really our plan," Clijsters said. "I just wanted to start these three tournaments and get back into the rhythm of playing tennis and get used to the surroundings again."

Her 18-month-old daughter, Jada, came down to the court to take part in the celebration with her mom.

"It's the greatest feeling in the world, being a mother," Clijsters said. "I just can't wait to spend next the few weeks with her and have her routine schedule at home again."

It was Clijsters' second major title — she also won at Flushing Meadows in 2005, her last appearance at the Open.

The 26-year-old Belgian was unseeded and unranked and needed a wild card to get into this year's tournament.

She's also the first woman not in the top 10 of the WTA rankings to win the U.S. Open.

Wozniacki, from Denmark, had never advanced past the fourth round of a Grand Slam event previously and became the first Dane to reach the final of one.

Federer 'shot' highlights men's action

On the men's side, Roger Federer and Juan Martin del Potro reached the U.S. Open final Sunday with straight-set victories over opponents Novak Djokovic and Rafael Nadal.

Defending champion Federer advanced to his sixth straight U.S. Open final after he defeated Serbia's Djokovic 7-6 (3), 7-5, 7-5 in the rematch of the 2007 Open final.

The world's No. 1 player punctuated his semifinal win with an unbelievable cross-court winner, hit backward between his legs from the baseline, to set up match point.

Federer told reporters he, like many other players, has practised the shot.

"A lot, actually, but they never work," he said. "That's why, I guess, it was the greatest shot I ever hit in my life."

Federer hasn't lost in the American major since losing to David Nalbandian in 2003.

"Right now, I'm pretty relaxed," Federer said. "We'll see how it goes when the sun comes up. I'd like to keep this going. It'd be great to get my first Grand Slam as a dad." Federer and his wife, Mirka Vavrinec, welcomed twin girls Charlene Riva and Myla Rose on July 23 in Switzerland.

Del Potro drubs Nadal to reach final

Del Potro beat Nadal 6-2, 6-2, 6-2 at Arthur Ashe Stadium to reach Monday's final of the tournament, whose schedule was turned upside-down by rain in the second week.

"I think this is the best moment of my life," del Potro said.

Nadal won the four of the first five career meetings between the players, but Del Potro has now won two straight, following up on a victory at the Rogers Cup in Montreal last month. Nadal has won the other three Grand Slam events but has never reached the final of the Open.

"I'm going to repeat: He played much better than me, and for that reason he beat me," Nadal said.

Del Potro, 21, opted to skip the Cincinnati tuneup to the Open, a decision that appears to have paid off. He can join Guillermo Vilas (1977) as the only Argentines to win the tournament.

Asked by reporters whether the match against Nadal was the best of his career, del Potro was quick to respond.

"I think so," he said. "It was so focused every moment because Rafa's a great player. He can run for five, six hours. I'm not very strong but I do my best, and I'm in the final."

Nadal, who has been battling knee and abdominal injuries, hunched over in pain after a double fault in the first set.

With files from The Associated Press