NEW YORK — No one saw this coming.
Not with Serena Williams so close to tennis' grandest of feats, to one of the greatest achievements in any sport, on her homecourt at the U.S. Open, no less.
Not even Roberta Vinci, the unheralded, unseeded Italian on the other side of the net.
Asked if she thought she had any chance of pulling off a momentous upset in the semifinals of the U.S. Open on Friday, Vinci replied after the match with admirable honesty.
"No," she said, shaking her head firmly. "When I wake up, I say, 'Okay, I am in the semifinals today. Try to enjoy it. Don't think about Serena.' I didn't expect that I (would) win."
But win she did, finishing off one of the most significant upsets in the history of tennis with another of her deft little shots that skidded just out of Williams' reach.
With that, Williams' bid to win the Grand Slam was done. A 2-6, 6-4, 6-4 loss will keep her from being the first woman to win all four major titles in a calendar year since Steffi Graf in 1988.
"I don't want to talk about how disappointing it is for me, if you have any other questions," Williams, the top seed, said at her news conference. "I thought (Vinci) played the best tennis of her career. … She played literally out of her mind."
Entering Friday, Williams was 43-1 at the U.S. Open when facing an unseeded opponent. Her only loss came in the 2009 semifinals against wild card Kim Clijsters. That also was the last time Williams had lost in the semifinals of any Grand Slam, snapping a streak of 11 straight wins in that round.
"I don't think I played that bad," Williams, 33, said. "I made more unforced errors than I normally would, but I think she just played really well. She did not want to lose (Friday), and neither did I, incidentally, but she really didn't, either."
Vinci had never before played in a Grand Slam semifinal; Williams owns 21 major titles. In four previous matchups, Vinci had never taken a set off Williams.
How little faith did even she have? Vinci, a 300-1 shot entering the tournament to win it all, said she had booked a flight home for tonight; the women's final is this afternoon. "Maybe I can still make it?" she joked.
In faltering English and shaking her head in disbelief during her oncourt interview, Vinci said, "This is an incredible moment for me. It's like a dream. I'm in the final. I beat Serena. … It is the best moment of my life. I'm sorry for the American people, for Serena, for the Grand Slam. But today's my day. Sorry, guys."
In the final, Vinci faces another Italian making her Grand Slam final debut: 26th-seeded Flavia Pennetta, who eliminated No. 2 Simona Halep 6-1, 6-3. This is the first major final between two Italians and the first between two women older than 30 in the Open era (since 1968). Pennetta is 33, Vinci 32.
Vinci's unusual style, full of slices and net rushes, kept Williams offbalance enough to cause problems. As the match wore on, Williams' legs seemed to get heavier and heavier. She kept getting caught flat-footed, struggling to get in the proper position to hit shots. Vinci, on the other hand, raced around the court, sending back everything Williams threw her way.
"In my mind I say, 'Put the ball on the court. Don't think about Serena in the other court. And run. Put the ball in the court and run,' " Vinci said.
Williams repeated her tournament-long contention that she never felt pressure. But Vinci said she thought Williams got hit by nerves as the match went on. Williams' coach, Patrick Mouratoglou, said, "I think she lost her way, mentally."
Williams still accomplished her second career Grand Slam this year, with her three major wins added to last year's U.S. Open. "So that's pretty good," she said.