NEW YORK — Serena Williams walked toward the line judge, screaming, cursing and shaking a ball in the official's direction, threatening to "shove it down" her throat.

On match point in the U.S. Open semifinals last night, defending champion Williams was penalized a point for unsportsmanlike conduct — a bizarre, ugly finish that gave a 6-4, 7-5 upset victory to unseeded, unranked Kim Clijsters.

The match featured plenty of powerful groundstrokes and lengthy exchanges. No one will remember a single shot that was struck, though, because of the unusual, dramatic way it ended.

With Williams serving at 5-6, 15-30 in the second set, she faulted on her first serve. On the second serve, a line judge called a foot fault, making it a double-fault — a call rarely, if ever, seen at that stage of any match, let alone the semifinals of a Grand Slam tournament.

That made the score 15-40, putting Clijsters one point from victory.

Instead of stepping to the baseline to serve again, Williams went over and shouted and cursed at the line judge, pointing at her and thrusting the ball toward her.

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

She continued yelling at the line judge, and went back over, shaking her racket in the official's direction.

Asked in her postmatch news conference what she said to the line judge, Williams wouldn't say, replying, "What did I say? You didn't hear?"

"I've never been in a fight in my whole life, so I don't know why she would have felt threatened," Williams said with a smile.

The line judge went over to the chair umpire, and tournament referee Brian Earley joined in the conversation. With the crowd booing — making part of the dialogue inaudible — Williams then went over and said to the line judge: "Sorry, but there are a lot of people who've said way worse." Then the line judge said something to the chair umpire, and Williams responded, "I didn't say I would kill you. Are you serious? I didn't say that." The line judge replied by shaking her head and saying, "Yes."

Williams already had been given a code violation warning when she broke her racket after losing the first set. So the chair umpire now awarded a penalty point to Clijsters, ending the match.

Clijsters will play for her second career major title today against No. 9 Caroline Wozniacki of Denmark, who beat Yanina Wickmayer of Belgium 6-3, 6-3 in the other rain-delayed women's semifinal.

Earlier yesterday, No. 3-seeded Rafael Nadal beat No. 11 Gonzalez, 7-6 (4), 7-6 (2), 6-0, in a match that began Thursday evening, was suspended that night because of showers in the second-set tiebreaker, and didn't resume until yesterday thanks to more rain Friday.

Weather permitting — two key words at Flushing Meadows lately — Nadal will face No. 6 Juan Martin del Potro in one men's semifinal today, and No. 1 Roger Federer will meet No. 4 Novak Djokovic in the other.