A snarly Serena Williams has refused to reveal how much it hurt after unseeded Italian Roberta Vinci spectacularly ended her quest for an elusive calendar-year grand slam sweep.

“I don’t want to talk about how disappointing it is for me,” Williams snapped at reporters in the wake of her shock 2-6 6-3 6-4 US Open semi-final loss to Vinci on Friday.

The centre-court boilover at Flushing Meadows is already being ranked the biggest upset in women’s grand slam history.

Ranked 43rd in the world and contesting her first grand slam semi-final, Vinci had never come close to nabbing even a set against the all-conquering world No.1 in four previous meetings.

But the 32-year-old rallied from a first-set mauling to shatter Williams’ bold bid to become the first player – man or woman – to win the Australian, French, US Open and Wimbledon crowns in a single season since Steffi Graf in 1988.

“Anyone else want to ask a different question than that?” Williams bristled when asked how she’d recover from the disappointment.

Riding a 33-match winning streak at the majors stretching back to a third-round loss to Alize Cornet at Wimbledon last year, Williams also missed the chance to join Graf atop the open-era grand slam leaderboard with 22 majors.

But the 33-year-old maintained the suffocating pressure to accomplish a feat achieved by only five players – Graf, Americans Don Budge (1938) and Maureen Connolly (1953) and Australians Rod Laver (1962 and 1969) and Margaret Smith Court (1970) – in more than a century hadn’t been a factor in her loss.

“I told you guys I don’t feel pressure. I never felt pressure,” the American said.

“I was just trying to win points at that match and win the match. Last questions?”

Vinci had no doubt, though, that Williams – who twice double-faulted and then fired a forehand long to gift the Italian the decisive third-set service break in the eighth game – was feeling the tension.

Asked how nervous she thought Williams was, Vinci said: “A lot.”

Williams’ last defeat at Flushing Meadows also came on 9/11 – the 10th anniversary of the attacks no less – to Australian Samantha Stosur in the 2011 final.

Once again, the 21-times major winner felt she lost out to an inspired performance from her underdog opponent.

“I thought she played the best tennis in her career,” Williams said.

“She’s 33 and she’s going for it at a late age. So that’s good for her to keep going for it and playing so well.

“Actually, I guess it’s inspiring. I think she played literally out of her mind.

“I don’t think I played that bad. I made more unforced errors than I normally would make, but I think she just played really well.

“She did not want to lose today. Neither did I, incidentally. But she really didn’t either.”

Williams called an end to her own press conference, just a dozen questions in, after hailing her “Serena Slam” – holding all four grand slam singles trophies simultaneously until being dethroned in New York – as a notable season highlight.

“I felt very happy to get that win at Wimbledon, you know. I did win three grand slams this year,” she said.

“Yeah, I won four in a row. It’s pretty good.”