At the last Olympics, Maurice Greene watched from the stands as Donovan Bailey tore down the Atlanta track in a world-record 9.84 seconds to claim the 100m gold.

At the time, Greene, who had bombed out of the US trials in the second round, wasn't really a sprinter fit enough to be in the same stadium as the powerful Canadian.

How times change. Greene has since smashed Bailey's world record, won back-to-back 100m world titles and made history as the first man to complete the 100-200m double at a world championship.

It's impressive work for an athlete who, only two months before his first world championship gold, was on the verge of quitting athletics at the age of 22.

Greene had turned up at the National Championships the year after the Atlanta Olympics with his career in tatters and his mental state shattered by a double family bereavement.

But rather than being the end of the track for Greene, the championships proved to be only the start.

The evening before his first heat, Greene's coach John Smith told him: ``This is the time to dig deep and find something in yourself.''

He didn't let him down.

Greene claimed the US national title in 9.90 seconds - 0.18seconds faster than his previous best - making him the third fastest American in history.

Less than two months later, the man nicknamed the 'Kansas Cannonball', continued his rise from obscurity by taking the world title in Athens.

This time it was Bailey who was left to watch, as Greene blasted past the reigning champion to capture gold.

When Greene returned to the Athens track on June 16 last year, he produced the most perfect display of 100m running ever witnessed. Greene, not happy with just Bailey's world title, snatched his world record as well.

The American ran a scorching 9.79 seconds, taking the biggest chunk off the world mark for three decades.

But for Greene, the time had a greater significance as 9.79 seconds equalled the time ran by a steroid-fuelled Ben Johnson when he ``won'' Olympic gold in Seoul in 1998.

The whole sorry incident shamed athletics but to sprinters it became the Holy Grail.

Greene later told the world and Johnson: ``I ran it and I'm clean. I have proved with this what I am.''

He was finally the undisputed fastest man on earth.

And two months later, he was still the fastest man on earth when he retained his world title in Seville.

The American took the gold with another stunning run, this time only 0.01 seconds outside his own world best.

Five days later, he claimed the 200m title to complete a unique sprint double.

Greene will concentrate solely on the 100m in Sydney after pulling up with a hamstring injury in the US trials during his much-hyped 200m showdown with Michael Johnson.

The only hope for his rivals is that the injury re-surfaces in the Games.

If not, then there will be nothing left for anyone to do but sit back and watch in awe as the 25-year-old powers into athletics history - again.