The 29-year-old superstar, widely seen as the greatest sprinter in history, stormed over the line in 37.27sec to trigger an eruption of adulation in the Olympic Stadium.
Japan’s quartet took a surprise silver in 37.60sec while Canada took bronze after the United States, who crossed in third, were later disqualified.
The victory saw Bolt complete a third consecutive clean sweep of the 100m, 200m and 4x100m titles — the so-called ‘triple-triple’ following his six gold medals in the 2008 and 2012 Games.
It leaves Bolt, who will retire in 2017, level with Carl Lewis and Paavo Nurmi on nine Olympic gold medals, a record for a track and field athlete.
“I’m going to stay up late and have fun,” said Bolt, who lingered on the track after his lap of honour, kneeling down to kiss the finish line amid chants of “Usain Bolt, Usain Bolt” echoed from the stands.
“I would never have thought I could do back-to-back-to-back Olympics. I never thought that. The first one I was just happy, the second one was a challenge and to come into the third one is just unbelievable. I hope I’ve set the bar high enough that no one can do it again.”
The relay gold was the final act of an incredible Olympic career that redefined athletics and has left commentators scrambling to find a new superlatives as each milestone came and went.
– ‘The man’s a genius’ -On Sunday Bolt became the first man in history to win a hat-trick of 100m gold medals.
He followed that up with Thursday’s barnstorming win in the 200m, sealing another never-before-seen treble.
“People always ask me if I’m unbeatable, but when it comes to a championship I think personally I am,” Bolt reflected Friday after an incredible 20th gold medal in Olympic and World Championships. The only blemish on an otherwise perfect record is a disqualification for a false start at the 2011 worlds in Daegu.
Friday’s triumph was potentially the most awkward, with Bolt’s gold medal hopes reliant on the performances of his team-mates.
But Asafa Powell, Yohan Blake and Nickel Ashmeade were in no mood to fluff their lines.
A superb third leg by Ashmeade ensured that Bolt had a precious lead after the final changeover.
From that point there was only ever going to be one outcome and Bolt powered home by three metres to universal delight.
“We wanted to win to make Usain immortal and he is immortal,” Blake said. “I’ve told him he should come back for 2020!”
Bolt added: “As soon as I got my hand on the stick I knew I’d won because there was no one on that leg who could outrun me today.”
Bolt will now set off a year-long victory tour that will culminate with the World Championships in London next August.
The Jamaican is preparing to exit with athletics fighting to restore credibility after a year dominated by doping and corruption scandals.
International Association of Athletics Federations president Sebastian Coe is adamant however that athletics will endure, despite the loss of its most charismatic leading man.
In an interview with AFP on Friday, Coe said Bolt had transcended his sport in a way that was comparable to boxing icon Muhammad Ali.
“The man is a genius,” Coe said. “There’s been nobody since Muhammad Ali who’s got remotely near to what this guy has done in terms of grabbing the public imagination.”
However, Coe argued that just as a new generation of boxers emerged after Ali’s retirement, so track and field would unearth new personalities after Bolt.
“It’s a massive gap, but it’s not a gap that is insuperable,” Coe said.
“You’re not going to fill that gap overnight, but there are great, talented athletes out there.”
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