It was supposed to be the biggest day in two small nations' Olympic history.

Within an hour of each other, over one lap of the London 2012 athletics track, in front of 80,000 animated fans, two young men with large feet and unfamiliar vests would be carrying the hopes of their respective island nations on their shoulders.

I doubt that everyone in their home-towns of Ponce (Puerto Rico) and Gouyave (Grenada) owns a television-set; but it is hard to imagine that anyone in either place was not watching.

What happened next illustrates the transformative quality, but also the cruelty, of an Olympic competition.

First up was Javier Culson, a chiselled giant from Puerto Rico with a white headband, pierced left eyebrow and a tattoo of the Olympic rings on his upper arm.

Javier Culson prepares himself for the 400m hurdles

His race was the 400 metres hurdles, the event of Ed Moses, John Akii-Bua and David Hemery.

He was favourite to emulate Uganda's Akii-Bua, the 1972 winner, by becoming the first Olympic champion from his country. 

Indeed, to listen to some people, you would have thought that he could not be beaten.

Wiser heads knew better: this was, after all, a hurdle race; anything could happen.

When I asked Hemery, the 1968 champion, who he thought would win, he mentioned four names:

"Javier Culson would be my first bet," the British athletics icon told me.

"I would love to see Dai Greene get to the podium.

"Angelo Taylor is Moses's pick.

"Félix Sánchez was fastest in the heats."

If Culson was in any doubt about the power of the forthcoming 50-second contest to transform his life, it must have vanished with the ceremony that took place in the moments before his start-time.

Usain Bolt, now a dual Olympic 100 metres champion, leapt to the top step of the podium to an oceanic roar and the flash of 50,000 cameras.

Lamine Diack, one candidate for the title of the most powerful man in athletics, hung an Olympic gold medal around the neck of another.

The Jamaican anthem played.

Minutes later, following another almost bestial roar at the introduction of Greene, one of British athletics's main pin-up boys, Culson and his rivals were off.

It started well enough: at halfway, the tall Puerto Rican looked to be in control of the race.

Dominican Republic's Félix Sánchez leading the men's 400m hurdles race

But then the imponderables that can bedevil any hurdle race started to unfold: Culson hit barrier seven; he lost his rhythm; coming off the final bend, it was suddenly clear that nobody was going to catch Sánchez, the runner in lane seven, the 2004 Olympic champion.

That the winner represented the Dominican Republic, a neighbouring country and another smallish island-nation, would have consoled 3.7 million watching Puerto Ricans not one jot.

As for Culson, well, it drains you this event; like many rivals, he spent long seconds splayed on the track before finally removing his bright scarlet running shoes and trudging off.

He had won Olympic bronze, one of just a handful in Puerto Rico's sporting history, but it felt like failure.

Afterwards, he was pitilessly hard on himself.

Javier Culson of Puerto Rico, Angelo Taylor and Kerron Clement of the United States stay on the track after completing the 400m hurdles

"It was a very bad run on my behalf.

"I'm not pleased with it at all.

"I lost my rhythm towards the end of the race and I couldn't get it back.

"I send my apologies to the people back home, but at least I made it to the final."

In the dressing-room, I am reliably informed that there were tears.

His time of 48.1secs was the same as Hemery's in 1968.

Silver medalist Michael Tinsley of the United States, gold medalist Félix Sánchez of Dominican Republic and bronze medalist Javier Culson of Puerto Rico

Come the medals ceremony, the acknowledgement of his achievement had started to take the edge off his disappointment.

Richard Carrión, the Puerto Rican master of the International Olympic Committee's (IOC) burgeoning finances and a possible successor to Jacques Rogge, touched his compatriot lightly but compassionately on both cheeks.

As Culson said later, "I was happy because I did get the bronze medal".

The tears, as seen by scores of millions of television viewers, were tears of relief and of regret and of joy, and they were shed by the winner Sánchez, in memory of his beloved "abuela" (grandmother).

No sooner had the Dominican dried his eyes than the moment of truth for another island athlete arrived.

Kirani James comes from an island called Grenada, far better-known for the production of world-class nutmeg than world-class 400 metre runners.

This self-assured young man, who doesn't turn 20 until next month, has a relentless quality to his running, though.

In the closing stages of a 400 metre race, when others are tying up, he usually looks like he could carry on indefinitely without losing pace.

And this was again how it turned out: spared the inconvenience of having to clear pesky hurdles and exploiting the unprecedented dearth of top-class US opponents, James strode to the win that had seemed his destiny.

Grenada's Kirani James wins the 400m final by a clear margin

It was Grenada's first medal of any description.

Afterwards, staring intently back at his media inquisitors, the teenager appeared preternaturally calm as he fielded questions about the fishing village where he was born and his labourer father.

"There is probably a huge street-party going on now," he speculated.

"I would like to thank my sponsors – Nike, Limetel Communications and Co-op Bank."

Later that evening, a party kicked off at the National Gallery on Trafalgar Square under Horatio Nelson's one-eyed gaze to "raise our glasses in honor of all the great Puerto Rican athletes who are representing the island at the 2012 Summer Olympic Games".

Kirani James holds up Grenada flag to crowds as he celebrates winning gold in then men's 400m

The timing of the event, straight after Culson's final, was plainly significant: the organisers had hoped to toast that first Puerto Rican gold medal.

It is, though, one of sport's most appealing qualities that it refuses to obey any script.

Culson, 28, says he plans to run in Rio in four years' time.

He even smiles at the prospect.

In 2016, he will still be younger than Sánchez is now.

Perhaps Puerto Rico's first Olympic golden moment will finally be celebrated on the Copacabana.

David Owen worked for 20 years for the Financial Times in the United States, Canada, France and the UK. He ended his FT career as sports editor after the 2006 World Cup and is now freelancing, including covering the 2008 Beijing Olympics and 2010 World Cup. Owen's Twitter feed can be accessed here