Serena Williams' U.S. Open title defense ended in bizarre, ugly fashion Saturday night, when she was penalized a point on match point after yelling and shaking her racket in the direction of an official who called a foot fault.

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Williams lost to unseeded, unranked Kim Clijsters 6-4, 7-5 in a taut semifinal.

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

Williams went over and shouted at the line judge, who walked over and reported it to the chair umpire. That led to the chair umpire awarding a penalty point to Clijsters, ending the match.

Williams already had been given a code violation warning when she broke her racket after losing the first set.