NEW YORK • Sport has a way of demonstrating that even the greatest champions are mere mortals and so it proved for Serena Williams on Friday.

A combination of spirited Italian fight, in the form of Roberta Vinci, and the pressure exerted by the tennis world expecting a new piece of history, wrecked aspirations of the first calendar-year Grand Slam for 27 years.

The last Grand Slam event of this year was supposed to be a celebration of one of the greatest American champions and a woman who took power tennis to new levels.

Williams had won the past three US Open titles and, to many supporters, it seemed a foregone conclusion that she would complete the set after claiming the Australian Open, French Open and Wimbledon crowns earlier this year.

Yet, like many an obscure Off-Broadway production, things do not always follow the script in New York.

Vinci, the world No. 43, had never beaten Williams in four previous meetings. By her own admission, she had been steamrollered by the world No. 1's velocity and brutality a few weeks ago in Toronto.

Yet, she provided probably the biggest of a catalogue of upsets for the 33-year-old American.

In years to come, people will look at the scoreline of 2-6, 6-4, 6-4 that denied Williams true legendary status and wonder how such a reversal could have happened.

The answer is quite simple: Anxiety and the fear of failure proved almost totally debilitating at a time when brute strength and clarity of thought would have sufficed.

This was a defeat that will probably haunt her for the rest of her days and Williams was understandably in an uncommunicative mood when asked to explain what had gone wrong.

"I don't want to talk about how disappointing it is for me," she said with the kind of glare that suggested that it was futile to try.

However, it appeared that the winner of 21 Grand Slam titles was almost in denial.

She insisted: "I told you guys I don't feel pressure. I've never felt that pressure to win here. I don't think I played that badly.

"I made more unforced errors than I normally would make but I think she just played really well.

"She did not want to lose. Neither did I, incidentally."

Yet, Williams made 40 unforced errors, twice as many as her opponent. She hit four double faults and was aced by a Vinci delivery timed at 135kmh.

And, most importantly, she seemed to suffer the kind of paralysis that hits a player when nerves take a hold. She was not moving her feet or hitting shots with any fluidity and Vinci is too experienced a competitor not to notice.

Vinci's victory ensured that the US Open became the first Grand Slam to stage an all-Italian final after 26th seed Flavia Pennetta, 33, produced the first upset of a memorable day at Flushing Meadows. She beat Romanian Simona Halep, the No. 2 seed, 6-1, 6-3.

Vinci, 32, a previous finalist in all four Grand Slams in doubles but never viewed as a serious contender for a singles title, kept her nerve while knowing that she was ruining one of the biggest stories in tennis.

"I'm sorry for the American people, for the Grand Slam, for everything, but today is my day," the player from Palermo, in Sicily, said.

"I woke up this morning and I told myself, 'Don't think about Serena, but just run and run'.

"And that is what I did.

"I am most proud of myself, my fight, my game."

THE TIMES, LONDON