As the world waited to watch Usain Bolt, a young man stunned the world, smashing one of athletics' most famous records.
South African 24-year-old Wayde van Niekerk stormed home off the final corner to streak to 400m gold in the Rio final in a world record of 43.03 seconds.
His time was 0.15sec quicker than the long-standing mark of Olympic legend Michael Johnson, whose previous world best came in Seville in 1999.
Van Niekerk also became the first man to win Olympic gold from the unfavoured lane eight.
Defending champion Kirani James of Grenada took silver in 43.76sec, with American Lashawn Merritt bronze (43.85).
"It's amazing," van Niekerk said.
"I really didn't care (about being in lane eight). Tonight was just about going out there and executing as well as possible."
A popular figure on the circuit, van Niekerk is known as a family man who often takes his mother on tour with him.
He is also trained by a woman 50 years his senior, 74-year-old great grandmother Ans Botha.
Despite van Niekerk being world champion, his underwhelming heat runs had meant all eyes were on James and Merritt.
The Grenadian James set off fast in lane five, Merritt on his coat-tails on the inside with van Niekerk running solo out wide.
The trio had produced one of the races of the year in the 400m final at the 2015 world championships in Beijing, all going under 44 seconds as the South African won the fastest one-lap race of all time.
And it was the same again in Rio, van Niekerk exploding around the last bend and holding his form through the line in an exceptional run.
"I'm happy to be part of a race that made history. We have put this sport on a pedestal," said James.
'THAT WAS A MASSACRE'
"I have never seen anything like that," Johnson told BBC, for whom he works as an analyst.
"It is amazing. That was a massacre by van Niekerk.
"This young man has done something truly special. He could go under 43 seconds - I tried and failed.
"Being out in lane eight helped him, he was away from James and Merritt. He was running a time-trial.
"That was some style he broke it in," Johnson added of van Niekerk, who made sprint history by becoming the first athlete to dip under benchmark times in the 100, 200 and 400m.
Having already clocked 19.94 seconds and 43.48sec in the 200 and 400m, van Niekerk timed 9.98sec in the 100m in March to set an athletics first.
Known as "Tannie Ans" (translated to "Auntie in English), Botha has been working with van Niekerk for three years - but has been a coach since the 1960s, when she initially worked with her own children.
Speaking in the lead-up to the Games about the responsibility that comes with handling a world and now Olympic champion, Botha told South Africa's City Press: "I wouldn't say I'm afraid ... but I have such a big responsibility to get this athlete to develop to his full potential.
"Also, I need to try to do my very best not to do something wrong that might break him. This medal was planned three years ago."
'IT WAS JUST MENTAL'
Merritt, who was Olympic champion at the Beijing Games in 2008 before serving a 21-month ban for testing positive for a banned steroid in 2010, hailed van Niekerk.
"It was a crazy race, a great moment in history. The world record was broken, the best man won," Merritt said.
Britain's Matthew Hudson-Smith finished last in 44.61sec, saying: "It was just mental, how quick that was, to be part of that.
"I thought I was gaining on them and then he (van Niekerk) kicked in the back straight and I thought, 'What was that?'"