Serena loses temper, then match

Williams, the defending champion, was defeated 6-4, 7-5 by unseeded wild card Kim Clijsters in a rain-delayed semifinal that will be remembered for one of the most bizarre and unusual finishes in tournament history.

Serving at 5-6, 15-30 in the second set, Williams was called for a foot fault on her second serve. The double fault -- Serena's fourth of the match -- made the score 15-40 and gave Clijsters match point.

Williams walked toward the line judge, who was sitting to her left, and shook her racket in anger.

"If I could, I would take this ... ball and shove it down your ... throat and kill you," Williams said.

The line judge approached chair umpire Louise Engzell and tournament referee Brian Earley came out from the tunnel to join the conference. Clijsters, appearing confused, stood 10 feet behind the baseline on her side, bouncing on her toes to try to stay loose in the chilly weather.

Following a one-minute conversation next to the umpire's chair, Williams was assessed a point penalty for her second unsportsmanlike conduct violation of the night, ending the match. Williams had received the first violation for smashing her racket after losing the first set on an unforced error.

Before the chair umpire could announce the ruling, Williams approached Clijsters, shook her hand and left the court while waving to the crowd. She exited to a chorus of ringing boos, as many fans thought she was forfeiting the match since the chair umpire made no announcement of the penalty.

"I don't think [Clijsters] understood it was a point penalty, which meant that I lost that point, which meant that I lost the match," Williams said. "I think maybe the umpire should have said something."

Williams would not repeat what she said to the line judge at the post-match press conference.

"What did I say? You didn't hear?" Williams said. "I'll let it go."

A foot fault occurs when a player's foot touches the baseline before the racket makes contact with the ball. It is widely considered a seldom-enforced violation: Williams said that she hadn't been called for a foot fault all year until the U.S. Open.

"There are rules, it's just unfortunate that it has to happen on a match point," said Clijsters, who defeated Williams for just the second time in nine career meetings.

The 26-year-old Belgian, who came out of retirement in August after following a 27-month retirement, will face ninth-seeded Caroline Wozniacki in Sunday night's final. Playing in her first U.S. Open since winning the tournament in 2005, Clijsters extended her winning streak here to 13 matches.

Clijsters, who married and gave birth to a daughter during her two-and-a-half years away from competitive tennis, is the first mother to reach a Grand Slam final since Evonne Goolagong Cawley won Wimbledon in 1980.

Having defeated Venus Williams in the fourth round of this year's tournament, Clijsters became just the third player to defeat both Williams sisters in the same Grand Slam event, after Martina Hingis at the 2001 Australian Open and Justine Henin at the '07 U.S. Open.

"Kim played an incredible match and she definitely came out with a plan," Williams said. "It's really good to have her back on the tour. Maybe we can get together have some calming lessons."