NEW YORK CITY—Civilization as we have known ended a few minutes before 3 p.m. on a hot Friday afternoon at the U.S. Open in Flushing Meadows, as Serena Williams blew the thrilling third set of her semifinal against Roberta Vinci.

Serving for the match, Miss Vinci did not allow the defending champion a single point and put the last two points over with deft placements that underscored how she was able to outfox a player who has won this tournament six times already and was the runaway favorite to triumph in the final.

In numbers terms, Miss Williams played the better match, with 16 aces to Miss Vinci’s single one and overwhelming her in winners (groundstrokes the other player has no chance of returning) 50-21. Despite the Italian’s tenacious will, which gave her the second set and forced a decider, the crowd buzzed with Serena-expectation until the very end.

To be sure, at 5-4 for Vinci, a hush fell over the expanses of the great Arthur Ashe Stadium, currently under renovation but fully functional (and full to capacity) as Miss Vinci won her first and then her second service points. Miss Williams, for the first time in the entire tournament, seemed to be holding back her biggest shots, hoping perhaps for the safer outcome of Miss Vinci’s nerve cracking under the strain.

This, it should be clear, is completely out of character for the great American player, who normally pulls out the stops and unleashes her superbly controlled fury when she needs to. Miss Vinci was thus given the opportunities she needed to use the talent for placement and maneuver that has made her one of the best doubles players on the Tour but only one of the better singles competitors.

Serena Williams overcame two tough opponents in three-set matches in earlier rounds, Bethanie Mattek Sands and her sister Venus (the latter in the previous match), and was widely expected to hoist the trophy on Sunday. In tennis, however, you never know and Miss Williams, exasperated by the endless hype, stated repeatedly that the world would not end, nor would her career, if she did not get the win and with it, the holy grail of tennis, the Grand Slam (holding all four majors in the same calendar year.)

She is a proud woman and has no false modesty about her sensational talent, but she also knows that most of those calling her the greatest tennis player, of any gender, or of all-time, are ridiculous and ignorant. This stupendous disappointment will do nothing to alter the human proclivity for sycophancy and hero-worship, and it scarcely matters.

Miss Williams will continue to impress us all—as will Miss Vinci, who goes into the final against countrywoman and pal Flavia Pennetta, winner of the other semifinal over the No. 2 seeded Romanian dynamo Simona Halep. The stadium will ring with cries of “Forza!” on Sunday, and the cries of “Let’s go!” of the great Serena will return next year to this greatest of all tennis tournaments.