Usain Bolt stormed past his rivals to claim a historic third straight Olympic 100 metres title and declared himself confident of becoming an "immortal" by the end of the Rio Games.
Hot on the heels of a sensational 400m world record by South African Wayde van Niekerk, the Jamaican surged past American rival Justin Gatlin to take the most prized Olympic gold in 9.81sec.
With one title in the bag, Bolt celebrated and turned his attention to completing the 100m, 200m and 4x100m 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 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.
Track massacre
Although way short of his 9.58sec world record, Bolt was happy with the performance.
He started slowly but reeled in the fast-starting Gatlin within 70 metres 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 Niekerk timed a lightning 43.03sec in the 400m, breaking American 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 Niekerk. 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 15.17m.
Athletics was hit by another doping sensation when the Court of Arbitration for Sport overturned a last-minute ban on Russian long-jumper Darya Klishina imposed by the IAAF world body.
Klishina had been the only Russian competitor accepted by the IAAF for the Olympics after inquiries found mass "state-sponsored" doping in the country.
Media reports said investigators found two bottles of Klishina's urine samples had been tampered with.
The CAS decided, however, that Klishina had met all the conditions set by the world body to take part in Rio. The women's long jump starts on Tuesday.
British surge
America's Simone Biles stayed on track for a record five gymnastics gold medals at a single Olympics when she clocked up her third, on the women's vault.
Max Whitlock won the men's floor exercise to become Britain's first Olympic gymnastics champion. He won a second in the pommel horse and was part of another golden day for the British team.
Wimbledon champion Andy Murray won his second straight men's singles tennis gold, beating Argentina's Juan Martin del Potro 7-5, 4-6, 6-2, 7-5 in a marathon final which drained both men.
"Today was a very up and down match, very stressful. Both of us had a lot of chances and it was a long and tiring match. I'm just glad I managed to get through it," said Murray.
Britain's Justin Rose became the first Olympic golf champion in 112 years, edging Sweden's Henrik Stenson on the final hole in a thrilling duel.
"Oh my God. That felt better than anything I've ever won. It was the best tournament I've ever done," Rose said.
A five-gold Sunday for the Brits put them a surprise second on the medals table with 15 victories, behind the United States on 26.
Rio Games security has proved a major headache for organisers, with several teams complaining of thefts and street crime in the recession-hit metropolis.
The latest to fall victim was US swimmer Lochte and three teammates, who said they were robbed at gunpoint by criminals who pulled over their taxi posing as police.
"The guy pulled out his gun, he cocked it, put it to my forehead and he said, 'Get down,' and I put my hands up, I was like, 'Whatever,'" Lochte told NBC News.
"He took our money, he took my wallet -- he left my cell phone, he left my credentials."