It was the last home game, and Jim Johnson, basketball coach at the Greece-Athena high school, thought: why not? His team were cruising to victory and there were just four minutes left on the clock. So he put in the 17-year-old kid who had worked so hard all season at keeping statistics, running the clock, and handing out bottles of water and endless encouragement. The gesture was meant as a reward. Instead, coach Johnson created a sporting fairy tale for the ages.
The kid in question wasn't just any kid. At the age of two, Jason McElwain had been diagnosed as autistic. So well, however, had he coped with the adversity that he became a hero to his schoolmates. He also became a relatively decent shooter of a basketball. But 5ft 6in is on the small side for a game where height counts for so much. However many times he tried out, the boy everyone knew as "J-Mac" could never quite get into the team proper - until those four magic minutes one evening last month. But only a Hollywood script writer could have imagined the real-life fantasy that would then entrance America.
In Jason's words, "I just caught fire, I was hot as a pistol". True, he missed his first two simple shots. But then, on the school gym floor, in front of 900 intensely involved spectators, he entered "the zone", the almost paranormal state where everything a sports player attempts turns to gold. His third effort rattled the board and dropped through the hoop. And then another, and another and another. By the time it was all over, Greece-Athena had put its local rival Spencerport to the sword with a 79-43 victory.
Jason alone accounted for 20 of the points, six long-range three-point shots and a two-pointer from closer in. Even though the Spencerport players didn't hustle him too aggressively, it was still four minutes of undiluted magic. When it was over, grown men were weeping as his teammates carried him off the court on their shoulders.
But this was only the beginning. If Britain has a soft spot for gallant losers and epic no-hopers, America's special weakness is for the feel-good happy ending, for the outsider who takes life's odds stacked against him and then tosses them to the four winds. In horse-racing there was Seabiscuit, the little runt of a racehorse who in the 1930s took on and beat the mighty War Admiral, champion of the country's snobbish racing establishment - and in doing so became a symbol of national resilience in the Depression era.
Or take the never-say-die heroics of baseball's Kirk Gibson, the injured Los Angeles Dodger who limped to the plate and then smashed a home run that set his team on the way to the 1988 World Series. From a TV commentator, the feat elicited one of the great lines of sports broadcasting. "I don't believe what I've just seen."
And so it was with Jason McElwain, on a mid-February evening in Rochester in upstate New York - an example not only of an event witnessed at firsthand yet which still beggars belief - but also of how a frightening and imperfectly understood medical condition need not be a barrier to success.
His feat has set in motion an extraordinary, "only-in-America" saga. The local papers were first to get hold of the story, then came national coverage, the interviews on the network news, the videoed clips of J-Mac's scoring spree shown over and over again. And, as was inevitable in a land where the distinctions between real life and the silver screen have long since disappeared, Hollywood got in on the act as well.
Disney has expressed interest. So too has none other than Earvin "Magic" Johnson, legendary superstar of the Los Angeles Lakers NBA team, now proprietor of a chain of urban cinemas, who called coach Johnson to discuss the movie rights to J-Mac's amazing story.
And so it has continued, right up to Tuesday when McElwain was summoned to a meeting at Rochester airport with the former baseball owner, incurable mountain biker and lifelong sports fan who is now the most important man in America. And such is J-Mac's fame and popularity that the person who had most to gain from the encounter was George W Bush.
As is well known, these are not the best of times for Mr Bush, beset by deepening crisis in Iraq, spurned even by members of his own party, and with an approval rating sinking close to Nixonian levels. This week the President was up in the Rochester area, trying to drum up support for a Medicare prescription drugs programme that has attracted only criticism since it was introduced in 2005. But before he got down to serious matters, he obeyed rule number one of the politician's survival manual. If you're not very popular yourself, start rubbing shoulders with people who are. Right now, that means J-Mac.
"I saw it on TV. Saw it on TV and I wept, just like a lot of other people did," he said in that weirdly syncopated style patented by presidents whose surname is Bush. "It's the story of a young man who found his touch on the basketball court, which in turn touched the heart of citizens all around the country."
It was also a cameo, too, of what Mr Bush sees as a uniquely American generosity of spirit that he never fails to extol - a story of "coach Johnson's willingness to give a person a chance, a story of Dave and Debbie's [the McElwain parents] deep love for their son." And as so often in America, the hucksterish and the noble march hand in hand. J-Mac's moment of glory is being celebrated in commemorative T-shirts, masks and mugs as well as a possible movie. Casual Friday, a Rochester-based clothing company, is donating 500 T-shirts. Each will be emblazoned with J-Mac's mantra - "Stay Focused", with a photo of the improbable basketball star being carried off the court in triumph.
But the message on the back of the T-shirt suggests that, just maybe, Jason's celebrity will last longer than 15 minutes, and that his accomplishment will help change attitudes about the neurological condition from which he has suffered all his life, for which no cure has yet been discovered. "J-Mac," it proclaims, "Six three-pointers for Athena ... One slam dunk for Autism."
Jason didn't talk till he was five - "and since then he probably hasn't stopped," says Dave McElwain. Some autistic children are withdrawn and utterly uncommunicative. Jason, who has a relatively mild form of autism, tends to the opposite extreme. "He's very social, he's a charmer," adds his father. At school, he has special-needs instruction, but attends regular classes as well.
In Jason's case, the illness shows itself in fearlessness, even recklessness, but he is also faithful to the obsessive focus and pursuit of a goal that is a hallmark of the autistic person. "He's never had any fear of doing anything," his father says, "or fear of what other people think."
Such imperviousness probably helped him put aside the mishap of missing his first two easy shots that now legendary evening, when other "ordinary" players might have lost heart.
The broader hope now is that Jason's compelling story will give yet more impetus to the search for a cure, and prod the federal government that Mr Bush runs to make more resources available to that purpose.
In cultural and social terms, autism may be more easily accepted than before. But severe cases can wreak havoc on entire families. One out of 166 children in the US is born autistic. The divorce rate for their parents can hit 90 per cent. If the emotional strains are devastating, the financial burdens can be no less ruinous. Home care and therapy for an autistic child can cost anything up to $90,000 (£55,000) a year - usually without insurance cover. If Jason McElwain's night of glory gives some people hope where there was none before, that will be its most precious legacy.
As for the young man himself, he professes to be unmoved by his celebrity, the film talk, the Presidential arm draped around his shoulder at Rochester airport, and the rest of the carry-on. His ambitions are unchanged: to get his high school diploma, go to community college, and then work at the local grocery store. Somehow though, you suspect, it will not be so simple.