Serena insists umpire 'cheated' her

She demanded: "What happened? That's my point. That ball was in. It's my advantage."

Williams then walked towards Alves, saying: "No, no, no, no, no. That was my point! What are you talking about? What's going on? Excuse me? That ball was so in. What the heck is this?"

Then she placed a ball on the court, and pleaded her case while pointing: "The ball landed here. That ball was not out. Are you kidding me? I'm trying to tell you: The ball was not out. Do I need to speak another language?" Alves responded: "Please calm down."

The incident was reminiscent of this year's Wimbledon, where Serena's sister Venus lost in the second round after Karolina Sprem was mistakenly awarded an extra point in the decisive tie-break.

Venus didn't argue at all, saying later she was confused, while umpire Ted Watts was kicked out of the tournament. Last night, Serena added: "At first, I thought it was another Wimbledon conspiracy. I'm very angry and bitter right now. I felt cheated. Shall I go on? I just feel robbed."

Williams won the US Open in 2002 but was denied the chance to defend her title because of knee surgery that forced her to miss eight months last year. The defeat means it is the first season since 1998 that neither Serena or Venus have won a grand slam title.

Eighth-seeded Capriati, who has never won her home Grand Slam, now faces a semi-final clash with Russia's Elena Dementieva.

The No6 seed overcame Amelie Mauresmo of France 4-6, 6-4, 7-6 in a match marred by double-faults and unforced errors.

The line-call row overshadowed a superb performance from Capriati. After being overwhelmed by Williams' power play in the opening set, the 28-year-old showed great determination to fight back and claim the second, capitalising on errors to level the match. After he good fortune in the opening game of the final set, she broke Williams again in the third game before serving out.

New York-born Capriati said: "I fought hard, and I prevailed because of that. I don't think one point changed the match."

"She came out firing and I started tight but I just tried to stay with her. I just didn't want to let it slip away. "You get second chance after chance after chance. I don't care what the tennis looks like, as long as it's gutsy."

Capriati will fancy her chances against Dementieva, who admitted feeling extremely jaded after her marathon quarter-final with No2 seed Mauresmo.

The Russian shrugged off 15 double faults and a stomach upset to reach the semi-finals for the second time and ruin the Frenchwoman's chances of her first grand slam title.

"I was dying out there at the end of the third set," said Dementieva. "But I survived because I'm Russian. I like all these struggles.

"I had a problem with my leg but I think it helped because I started to serve and volley and won the second set like that. That's really interesting because you have to think a lot and be smart on the court."

Mauresmo, who would have taken over as world No1 next week if she had won the match, said: "I'm pretty disappointed and a bit angry with myself because I didn't take my opportunities."