Jamaican Usain Bolt has retained his Olympic 100 metres crown in spectacular style.
He crossed the finish line in 9.63 seconds becoming the first man to win back-to-back titles on the track.
It was the second-fastest time ever run for the 100m, and made Bolt the first man to win back-to-back titles on the track, even though he did not beat his world record of 9.58 seconds.
World champion Yohan Blake made it a Jamaican 1-2 when he won silver in 9.75 seconds and 2004 Olympic champion Justin Gatlin of the United States grabbed bronze in 9.79 as the first seven men all broke 10 seconds. For both men, the times were personal bests, Reuters reports.
Tyson Gay finished fourth in a season's best 9.80 seconds with fellow American Ryan Bailey fifth in an equal personal best of 9.88.
In the semi-finals, Gatlin won the first of three semi-finals in 9.82 seconds; Bolt won his heat pulling up in 9.87; and the final heat went to Blake in 9.85.
In that semi-final Bolt appeared lithe and loose and easing up with 30 metres to go.
The final was all about Bolt, who has said repeatedly that he needed back-to-back titles to cement his place among the sport greats.
Carl Lewis is the only other man to win two Olympic 100m titles and the American's second gold came only after Ben Johnson was disqualified for doping.
Bolt was slow out of the blocks on in the final and trailed Blake, who beat him in the Jamaican trials, and Gatlin, back in the mix after serving a doping ban.
But his massive stride reeled them in and he roared through the line, barely easing his speed as he tore round the bend to soak up the adulation of the delirious crowd.
"When I went out in the first run, I felt 'I can do this,' Bolt told the BBC in reference to his opening heat on Saturday.
"I was slightly worried about my start, I didn't want to false start again. So I think I sat in the blocks a little bit, I don't think it was the best reaction in the world, but I executed and that was the key.
"Remember I told you my coach said 'stop worrying about your start', the best of your race is at the end, that's where you rule. So I stopped worrying about the start and I executed, so it worked."
Bolt, who was disqualified from last year's world championship final for a false start, will now bid to complete an unprecedented double-double by retaining his 200 metres title and will also seek a sixth sprint gold in the 4x100 metres relay.
"Usain knows what it takes, he is a world beater and he is the fastest man in the world," said Blake. "But I got a medal in my first Olympic games and a lot of that is down to Usain and our coach."