South Africa’s Wayde van Niekerk broke Michael Johnson’s 17-year-old 400m world record to sensationally win Olympic gold at Rio 2016.
The 24-year-old finished in 43.03 seconds, 0.15 quicker than the time Johnson clocked in Seville in 1999.
Grenada’s Kirani James, the London 2012 champion, finished 0.73 behind to take the silver medal, with American LaShawn Merritt in bronze.
“It was a massacre,” said Johnson, who won two Olympic 400m titles.
“Van Niekerk is so young, what else can he do? Can he go under 43 seconds? It is something I thought I could do, but never did.
“Usain Bolt will be retiring soon, this could be the next star.”
Van Niekerk, who won South Africa’s first gold medal of the Games, said: “I have dreamed of this since I was a kid.
“I believed it was possible. I am just glad things went my way. I thank Michael Johnson for setting such a great example for us. I just did my best.”
Van Niekerk’s earlier runs in Rio gave little indication of what was to come.
He beat James and Merritt at the World Championships in Beijing last year, with all three going under 44 seconds, but qualified fifth fastest for the final.
James set off fast at the start of the race, but Van Niekerk, in lane eight, powered around the final bend to beat his previous personal best by 0.45.
Not only was it his first Olympic medal, he also became the first man to win an Olympic 400m title from lane eight.
Van Niekerk was still trackside doing interviews when Usain Bolt won 100m gold for the third straight Games half an hour later.
Bolt interrupted his own victory celebration to seek out the South African, who spent time in Jamaica working with Bolt and his coach, Glen Mills.
“He’s very fast and keeps on going,” said Bolt, who claimed he had predicted Van Niekerk would break the world record. “I wasn’t really surprised he got it.”
Silver medallist James added: “I’m happy to be part of a race that made history. We have put this sport on a pedestal.”
Great Britain’s Matthew Hudson-Smith, who finished last in 44.61, said: “It was just mental how quick that was.”