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

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

Clijsters made history Sunday 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.

Guess what mommy got for you, sweetie! A Grand Slam title.

“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.”

Talk about your quick transitions.

It was all quite a different scene from the night before, when Clijsters’ semifinal win over Serena Williams was decided on 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.

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. Meanwhile, Serena Williams’ tirade on Saturday may have gotten her into deep trouble beyond the penalty point assessed that cost her the match.

Early Sunday evening, the USTA announced that it had fined Williams the maximum $10,000 for a profane tirade. But that wasn’t the end of it.

According to a news release, the USTA said: “The Grand Slam Rule Book also allows for an investigation to be conducted by the Grand Slam Committee Investigator if the behavior of Ms. Williams warrants consideration as a Major Offense for which additional penalties can be imposed. This investigation has now begun.”

This opens the way for a possible suspension after the Open and a potential fine of $250,000 by the Grand Slam Committee.