According to some reports she told her: "If I could, I would take this ... ball and shove it down your ... throat and kill you."

The lineswoman then ran up to umpire Louise Engzell to report the incident which brought tournament referee Brian Earley onto the court.

Williams again remonstrated with the lineswoman over her version of what had happened, at one point telling her "I never said I would kill you."

She then stormed off to the other side of the net to shake hands with Clijsters when she understood she had been penalized a point on match point for verbal abuse.

"I said something that I guess they gave me a point penalty for. Unfortunately it was on match point," she said.

Williams, an 11-times Grand Slam winner, who has just brought out a autobiography ironically titled "On the Line," said that she had never been in a fight in all her life and would never have threatened anyone. But she did say that yelling at linesmen was relatively commonplace among top tennis players. "Well, how many people yell at linespeople?

"All the people that, you know, kind of yell at linespeople, I think it kind of comes sometimes.

"Players, athletes get frustrated. I don't know how many times I've seen that happen."

Williams had appeared edgy and uncomfortable throughout a match that had originally been scheduled for Friday afternoon but had been repeatedly delayed because of rain that swept in over the New York area from late Thursday and wiped out all play on Friday and most of Saturday.

The game eventually got underway in damp, cold conditions after 9:00 p.m. on the Arthur Ashe Stadium court and Williams was under pressure from the start.

She drew a first code violation from the chair umpire for angrily smashing her racquet on the ground after netting a backhand to concede the first set and her mood seemed to fluctuate between aggression and despair.

"I'm a really, really intense player, and I always have been," she explained when asked about her mood.

"I mean, my idol is John McEnroe and Martina Navratilova, so and Monica Seles, actually. It's kind of a big mixture."

Asked about her opinion of what happened at the end of the match, Clijsters said she had taken a back seat. "To be honest with you, I didn't even want to be involved, just because in my mind I was still focused. Okay, Kim, don't lose focus. You still need to win this last point here," she said.

Cjisters was to play against Danish teen Caroline Wozniacki, never before in the last eight at a Grand Slam, who advanced to the U.S. Open final by defeating Belgium's 50th-ranked Yanina Wickmayer 6-3, 6-3, on Saturday.