Bitter, angry, upset and cheated were a few of the words Serena Williams used to describe her feelings after a controversial quarter-final defeat by fellow American Jennifer Capriati at the U.S. Open on Tuesday.

The twice former champion crashed out 2-6, 6-4, 6-4 in a match that will live long in the memory not only for the ferocity of the tennis but several dubious umpiring decisions, one of which had Williams saying the official had gone "temporarily insane".

After the opening two sets of the heavyweight battle had been shared, the match ignited in the first game of the decider when Williams crunched a backhand winner inside the sideline.

The line judge correctly signalled the ball was in only for Portuguese umpire Mariana Alves, sitting the other side of the court, to call "advantage Capriati".

Williams's disbelief turned to fury as Alves refused to change her decision but her protestations were to no avail as she went on to lose her serve.

After two more breaks of serve, Capriati had another slice of fortune when serving for the match at 5-4. This time, with the score at 0-15, a Williams winner was called wide when television replays showed it had landed on the line.

With the stadium erupting, Capriati held her nerve to clinch victory while Williams stalked off court shaking her head.

"At first I thought it was another Wimbledon conspiracy," Williams told reporters, referring to an incident earlier this year when sister Venus was the victim when an umpire called an incorrect score during her match against Karolina Sprem.

"I thought she (Alves) just got the score wrong and I just wanted to clarify that I had won the point naturally because I know my shots and I saw the ball. And I knew it was in.

WTA APOLOGY

"(The umpire) said she overruled. I said, 'How could you overrule a line that far away? Why would you even overrule that shot? It didn't even touch the line'."

Williams, who said she had received an apology after the match from the WTA, said the call changed the way she played in the third set.

"Honestly, I began to think, 'Okay, well, I'm not going to go for the lines. I'm not going to go for my shots.' I just thought maybe they would call it out. So I started to play a little more safe.

"I thought she had got the score wrong. I was going to call the referee. But she claimed that, you know, I guess she went temporarily insane.

"I'm very angry and bitter right now, I'm extremely upset. I feel cheated. Should I keep going?"

Williams, who committed more than 50 unforced errors during the two-hour epic, did admit the line calls were not totally to blame for the loss of a match she dominated early on.

"I should have closed her out in the second set," she said. "If I had three less (unforced errors) maybe I would have won.

"I don't want to make excuses and say I lost because the umpire cheated me, which probably does have a major factor in it. But at the same time I think you've got to give credit to Jennifer, I guess.

"Like I said, she played good and I pretty much dug my own grave and got in, pretty much covered myself up with the dirt. I pretty much killed myself out there."

Asked her feelings towards the umpire, Serena said: "Obviously I don't want her to umpire my courts any more, she's obviously anti-Serena."