Sprint icon Usain Bolt clinched a third straight Olympic treble on Friday night, winning his ninth gold medal overall as part of Jamaica's 4x100-metre relay in his Games farewell.

Anchor leg runner Bolt teamed up with Asafa Powell, Yohan Blake and Nickel Ashmeade to steam to victory in 37.27 seconds in what was his last career race at the Olympics.

Japan stormed to silver in an Asian record of 37.60 and Canada took bronze in 37.64 after original third-place finishers the US were disqualified.

Bolt also has 100m/200m/4x100m trebles from 2008 and 2012, and holds the world record in all three events.

"There you go, I am the greatest," Bolt said. "I am just relieved. It's happened. I am just happy, proud of myself. It's come true."

The world's greatest sprinter, who also boasts 11 world titles, has now matched American Carl Lewis with the nine golds.

Lewis famously won the 100m, 200, 4x100m and long jump in 1984, adding three more long jump golds, two relays and another 100m at later Olympics.

Bolt, who turns 30 on Sunday, said after Thursday's 200m win that Rio would be his last Olympics but that he planned to compete at next year's worlds in London.

The US won the women's relay after only making the final in a re-run; Kenya's Vivian Cheruiyot grabbed 5,000m gold after a remarkable comeback against Ethiopia's Almaz Ayana; Ekaterini Stefanidi topped the women's pole vault; and Dilshot Nazarov got Tajikistan's first ever Olympic gold by dominating the hammer throw.

In the morning, world champions Matej Toth of Slovakia and Liu Hong of China added Olympic gold to their world titles in the 50km and 20km walks respectively.

Allyson Felix became the first female Olympian to get five gold medals when she won the women's relay together with long jump champion Tianna Bartoletta, English Gardner and Tori Bowie, a 100m silver and 200m bronze medallist, in the second fastest time ever, 41.01 seconds.

Felix now has five golds and three silvers from three Olympics.

Jamaica, with 100m and 200m Olympic champion Elaine Thompson, had to settle for silver in 41.36 and Britain took bronze in 41.77.

The US team dropped the baton in the heats but were allowed a re-run because Felix was obstructed by a Brazilian in the incident, and they qualified by time for the final.

In the 5,000m, Ethiopia's Ayana, who had smashed the 10,000m world record for gold on Saturday, broke the pack after some 1,800m and led by as much as 40m.

But Cheruiyot and countrywoman Hellen Obiri roared back and ran past the tiring Ayana with 600m left, with Cheruiyot winning in 14 minutes 26.17 seconds, more than three seconds ahead of Obiri and the world champion Ayana taking bronze almost eight seconds behind.

Cheruiyot claimed her first Olympic gold after silver and bronze in 2012, to go with a 5,000m and 10,000m double gold at the 2011 worlds, and a 10,000m gold from last year.

"Almaz is such a great athlete, we thought she would win again. She got ahead but then I thought, 'She's not moving'. I was working and I went past her. I'm so happy," Cheruiyot said.

The European champion Stefanidi won the pole vault with 4.85m, on countback against American season leader Sandi Morris, with both clearing 4.85m. Eliza McCartney took bronze for New Zealand with 4.80m.

Stefanidi's victory came a few hours after pole vault queen Yelena Isinbayeva said during her retirement announcement that the Olympic competition was devalued by her absence in connection with a doping-related ban on Russian athletes.

"I don't feel like it is an incomplete gold," Stefanidi insisted. "It is a little upsetting to all of us because we had nothing to do with this decision."

In the walks, Toth got Slovakia's first ever athletics medal when he denied Australia's Jared Tallent a first outright title, winning in 3 hours 40 minutes 58 seconds. Japan's Hirooki Arai took bronze after being temporarily disqualified.

Tallent was promoted to gold from London 2012 after the initial Russian winner Sergey Kirdyapkin was disqualified, and only received the medal two months ago.

"I wanted to win. That was the main aim after what happened in London. Getting the gold medal so late, and to be an Olympic champion for more than a few months," Tallent said.

The athletics events in the stadium conclude Saturday with seven finals, the women's 800m, 4x400m and high jump; and the men's 1,500m, 5,000m, 4x400m and javelin.

The final athletics event of the Rio Games is the men's marathon on Sunday.

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