Usain Bolt stormed past his rivals to claim a historic third straight Olympic 100 meters title and declared himself confident of becoming an "immortal" by the end of the Rio Games.

Hot on the heels of a sensational 400-meter world record by South African Wayde van Niekerk, the Jamaican surged past US rival Justin Gatlin to take the most prized Olympic gold in 9.81 seconds.

With one title in the bag, Bolt celebrated and turned his attention to completing the 100 meter, 200 meter and 4x100 meter gold medal sweep at three consecutive Olympics.

"Somebody said I can become immortal. Two more medals to go, and I can sign off. Immortal," said Bolt, who has said this will be his last Olympics.

Bolt said he had been "shocked" at the booing directed at Gatlin, who has twiced been banned for doping, but insisted he had focused on the victory that left him out alone in the 120-year history of Olympic sprinting.

Although way short of his 9.58-second world record, Bolt was happy with the performance.

He started slowly but reeled in the fast-starting Gatlin within 70 meters and eased up, thumping his chest as he crossed the line. Canada's Andre de Grasse took bronze.

"It was brilliant. I didn't go so fast, but I'm so happy I won," he said.

Minutes earlier, Van Nie-kerk timed a lightning 43.03 seconds in the 400-meter, breaking US runner Michael Johnson's 17-year-old record.

"I have never seen anything like that," Johnson told the BBC. "It is amazing. That was a massacre by Van Nie-kerk. This young man has done something truly special."

Kenya's Jemima Sumgong won the first athletics gold of the day, making light of searing heat to triumph in the women's marathon.

Colombia's world champion Caterine Ibarguen won the women's triple jump with a leap of 15.17 meters.