Usain Bolt produced a moment of human ultimacy in Rio on Sunday night, pulling himself up to his full thrilling height in the final few strides of the 100m to claim an unprecedented third Olympic gold medal in his final Games.

It was a moment to garland even this preternatural athletic career, the photo-finish snapshot showing every other runner in the field leaning forward at the line, straining towards the lone upright figure out front like a beautifully constructed classical frieze. Bolt didn’t ease off as he took the gold, instead pumping his chest with what looked less like joy, more a pure competitive rage, veering away across the royal-blue Olympic track pursued by photographers, cameras, stewards, the eyes of the world.

This was in many ways Peak Bolt, the last Olympic appearance in the ultimate event for the human race’s ultimate speed freak. Bolt is now out on his own, buffered by the clear blue water of an unheard-of third straight Olympic gold. All high-end sport involves a drive towards some vision of perfection, just as the 100m is in effect the search for 45 perfect strides, or 41 if you happen to be a 6ft 5in (195cm) Jamaican uber-athlete.

A photo-finish freezeframe of the Olympic 100m final in Rio, with Bolt upright and out in front. Photograph: Handout/Reuters

Never mind the eternal struggle with his start, the technical snags and clogs presented by his own height, Bolt can now justifiably be called the greatest speed athlete ever, the closest to a loose, rangy kind of completeness.

From here those who come will always strain towards him, always chasing that lone upright figure out in front. True to form Bolt was utterly captivating not just during, but before and after the race as he waved and posed and horsed around with the mascot, the flags, and pretty much anyone who asked.

This is a Games to drink in every last one of these Bolt-isms, to suck the sweetness from the brilliant fluke of having such an uplifting, utterly cloudless all-time champion among us. The contrast between the flowing brutality of Bolt on the track and his good humour, star sheen and general ditzy sense of fun has been as striking as ever in Rio.

Nobody in any sport has ever made being this good and this ruthless look so soft, so recognisably human. And yet for all that it wouldn’t be an Olympic 100m final without some lingering questions.

One of these has at least been answered. We can now say Rio 2016 will not at any stage fill its Olympic stadium. If they won’t come for Bolt they won’t come at all. Here the stands of the made-over Botafogo football stadium were three-quarters full. A patchwork of blue plastic seating could still be seen even as the stadium cracked and swooned on a muggy, oppressive night in Rio, leant a thrilling skein of Olympic authenticity by the presence in the wings of the most captivating athlete of his generation.

As the 100m men emerged for the final act of the night, the air seemed to disappear out of this grand concrete bowl. The American Justin Gatlin, billed without nuance or sympathy as a kind of anti-Bolt, a convenient super-villain for the wider audience, drew some graceless boos from the crowd.

Bolt acknowledges some people in the crowd after his win. Photograph: Xinhua / Barcroft Images

Bolt was was greeted with a white noise of adulation, the right man in the right place at the right moment, here to compact his own entire hidden backstory of grind and guts and sweat and anxiety into nine seconds of legacy-minting sporting history. No pressure, then, Usain.

Gatlin sucked his gums as his name was called. Yohann Blake, Bolt’s training partner, prayed pointedly. Bolt smiled and reeled off a dutiful twirl move or two, all part of the dance of intimidation.

Nervous? No, you? Gatlin was up first, legs spread, pumping away in the familiar supercharged twerk of his start. Bolt’s start was the usual compromise with his physique, resembling as ever a startled Tyrannosaurus Rex scrabbling up out a reed bed in pursuit of a passing squadron of raptors. Bolt’s start has always been a problem. Bolt has always been a problem. He will remain one even in leonine Olympic retirement. The problem with Bolt is simply how good he is.

There remains a basic spasm of accommodation in absorbing and processing such exceptionalism in a sport where history assures us even touching greatness – one or two fine exceptions aside – is to emerge somewhere down the line as tainted, boosted, chemical-fed. Of the 30 fastest 100m times ever, nine – including the top three – are by Bolt. The other 21 were run by athletes who have tested positive at some point for doping. In terms of clean speed the order goes: Bolt fresh air, more fresh air, the rest of the human race. What are we supposed to make of this surplus brilliance?

Here is an athlete who is not just better, but jaw-droppingly supreme even among dopes and cheats. The human brain struggles to process such anomalies. We seek the shortest grubbiest explanation. Bolt has never been touched by this. It is part of the tragedy of the sport, a beautifully pure thing made toxic, that even Bolt must carry this shadow with him at one remove.

Something else stood out in Bolt’s moment of crowning glory in Rio.

This was an old man’s race. Bolt turns 30 in a week. Gatlin, who took the silver is 34, the oldest man ever to get Olympic 100m gold or silver. Bolt and Gatlin together are the oldest top two in Olympic 100m podium history, and by some way on the overall spread. The bronze medalist Andre De Grasse of Canada is 13 years younger than Gatlin, but he finished a 10th of a second off the front. Beyond this there have been 55 sub-9.81 second runs in 100m history, but only Bolt and Gatlin have done it in the last four years. “Speed is the last excitement left, the one thing we haven’t used up,” Don DeLillo wrote in End Zone. But have we?

Even here there was a slight sense of greedy anti-climax that Bolt hadn’t produced one of his genuinely stunning times. In those oddly dreamy seconds mid-race as Bolt rolled himself up to his full height there was a feeling he would slip the gears and drive out of the pack.

It came in the end. Not perhaps with the insatiable surge of his real pomp, but with a kick of the turbo thirty metres out, nudging out in front and taking it by a margin of 0.08 seconds.

Cue delirium, and for Rio 2016 a very timely sense of genuine A-list event glamour. For Bolt next up is the 200m here, then another world championships next year, with the spectacle of a planned retirement in 2017. The paradox of his own mind-boggling greatness will rumble on at the fringes, an athlete who has defied not just all previous physical rules but the tawdriness of his own sport; and who will now leave these Games as an all-time talent fully realised.