Roberta Vinci of Italy is congratulated by friends after she defeated Serena Williams of the US in their women's singles semifinal match at the US Open Championships tennis tournament in New York, September 11, 2015. [Photo/Agencies]

Steady Italian

Following a dominant first set from Williams, the Italian made a fifth-game service break stand up to force a third set as the heavily-favored American racked up unforced errors as she tried to overpower her opponent.

Williams destroyed her racket with a frustrated smash before the start of the climactic set and tried to lift herself to victory with clenched-fist roars on winning points as the third set unfolded.

But the steady Italian refused to buckle.

Williams broke for an early 2-0 lead but Vinci broke right back when the top seed double-faulted.

The world number one, who hammered in 16 aces, double faulted twice in the seventh game when Vinci broke her again for a 4-3 lead in a game in which she celebrated a forehand volley winner by waving her arms for some appreciation from the crowd.

Three games later, the Italian cooly half-volleyed a winner

to cap the extraordinary result.

"When I wake up today I say, 'OK, I have a semi-final today, try to enjoy. Don't think about Serena. Play, enjoy. I did not expect that I won."

Vinci said the tension was palpable.

"At the end we had a lot of pressure, I think both (of us)," she said.

"In my mind I say, 'Put the ball on the court, don't think. Try to put all the balls on the court. Don't think about Serena in the other court. And run.' And then I won."

The beaming Vinci was almost apologetic about ending the single season Grand Slam run of Williams.

"Sorry guys," Vinci said.

"For the American people, for Serena, for the Grand Slam and everything. But today is my day. Sorry guys," said the Italian, who was showered with an Arthur Ashe ovation.