NEW YORK — Kim Clijsters cradled the baby in one arm, the trophy in the other.

The joy of motherhood. The joy of winning the U.S. Open.

Clijsters made history last night, capping a comeback from two years out of tennis to become the first unseeded woman to win the Open — and the first mom to win a major since 1980 — with a 7-5, 6-3 victory over No. 9 Caroline Wozniacki.

When it was over, Clijsters collapsed to the ground and started crying — tears of joy, probably mixed in with a little bit of shock, too. Her 18-month-old daughter, Jada, watched from a suite with a pacifier in her mouth, but later came down to the court to take part in the celebration.

"It still seems so surreal," Clijsters said. "Because it wasn't in the plan. I wanted to come back here, get a feel for it, play a Grand Slam so I wouldn't have to come back next year and learn the new experiences all over."

Talk about your quick transitions.

It was all quite a different scene from the night before, when Clijsters' semifinal win over Serena Williams was closed out on a foot fault, an outburst and a point penalty, and the 26-year-old Belgian stood behind the baseline, looking bewildered as Williams ran over to shake her hand.

Williams' tirade may have been the talk of the U.S. Open. But Clijsters was the winner.

This was her second U.S. Open title, the other coming in 2005 — her last appearance at Flushing Meadows and before a spate of nagging injuries eventually drove her out of the sport and led her to start a family. These days, she has her baby's name tattooed on her left wrist, near the scar from an operation she needed back in her first career.

When she came back, she was "starting from zero," she said. The work to get back in shape was not pretty.

Clijsters beat both Williams sisters and two players seeded in the teens. She matched Venus and Serena power shot for power shot and showed she could play Wozniacki's patient game — and play it better.

"She's playing because she thinks it's fun and because she likes it," said Wozniacki, who is too young to have played Clijsters during her first career. "I really think she might be a better player now than she was before."

SERENA GETS FINED $10,000 FOR TIRADE

Serena Williams' profanity-laced, finger-pointing tirade at a U.S. Open linesperson drew a $10,000 fine yesterday, and more punishment could follow from a broader investigation into what the head of the tournament called her "threatening manner."

The fine — not quite 3 percent of the $350,000 in prize money Williams earned by reaching the semifinals — is the maximum on-site penalty that can be issued for unsportsmanlike conduct at a Grand Slam tournament.

"The average individual would look at that and say, 'A $10,000 fine for what she did? What are you guys, crazy?' The answer is: the process isn't over," tournament director Jim Curley said in an interview with The Associated Press.

Bill Babcock, the top administrator for Grand Slam tournaments, will review what happened Saturday night, when Williams yelled at a linesperson who called a foot fault with the defending champion two points away from losing to Clijsters in the semifinals.

If Babcock determines Williams committed a "major offense," she could be fined all of her prize money from the tournament.

Williams also was docked $500 for smashing her racket after the first set of the match. Because she was issued a warning then, her later actions resulted in the loss of a point.

Williams released a statement through a public relations firm, acknowledging that "in the heat of battle I let my passion and emotion get the better of me and as a result handled the situation poorly."

She did not apologize for the outburst.

FEDERER IN; NADAL FALLS IN SEMIFINALS

And for his next act ...

Top-seeded Roger Federer punctuated his latest U.S. Open victory yesterday with a shot he called, quite simply, the greatest of his life: a between-the-legs, back-to-the-net, cross-court winner from the baseline.

A point later, with the crowd in hysterics and fourth-seeded Novak Djokovic still in shock, the world's top-ranked player closed out the victory, 7-6 (3), 7-5, 7-5, to move one win from his sixth straight U.S. Open title.

OK, who's got next?

Juan Martin del Potro is the lucky guy whose first career Grand Slam final will come today against Federer, who made his 17th in the last 18. Earlier in the day, No. 6 Del Potro stunned No. 3 Rafael Nadal, 6-2, 6-2, 6-2.

The winner Federer hit to set up match point was the kind of shot every tennis player has tried, but the best player in the world practices it, too.

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

AP writer Howard Fendrich contributed to this report