Yet another gold medal for the incomparable Usain Bolt was no surprise, but Wayde Van Niekerk stunned the world with a remarkable 400m win.
Usain Bolt made history at the Rio Olympics by claiming a third men's 100 metre title, after Wayde van Niekerk had ascended to stardom with a remarkable record-breaking display over 400m.
Bolt surged past arch rival Justin Gatlin in the closing stages of Sunday's blue-riband event, a time of 9.81 seconds enough to keep athletics' biggest superstar - the winner of 100m, 200m and 4x100m relay gold at the previous two Olympics - on track for an incredible 'triple-triple'.
Gatlin and Canada's Andre De Grasse claimed silver and bronze respectively as six of the eight finalists broke the 10-second barrier, but the 100m final took place with many spectators still in shock following Van Niekerk's heroics less than half an hour earlier.
In one of the most spectacular displays imaginable, reigning world champion Van Niekerk dominated the 400m final from lane eight, leaving pre-race favourites Kirani James and LaShawn Merritt trailing in his wake and shaving 0.15secs off Michael Johnson's world record as he stopped the clock at 43.03secs.
Sunday's other track and field gold medallists were Caterine Ibarguen, who won the women's triple jump with a final leap of 15.17m having finished second in London four years ago, and Jemima Sumgong, Kenya's first victor in the women's marathon.
World record holder Genzebe Dibaba was the fastest qualifier for the women's 1500m final, while Allyson Felix ran a season's best of 49.67secs to top the list of finalists for the women's 400m.
Mutaz Essa Barshim, Bohdan Bondarenko and Brandon Starc - the brother of Australia cricket international Mitchell - were among 11 men to clear 2.29m in qualifying for the men's high jump, with a further four competitors making the final.
Somehow, Bolt's history-making triumph did not provide the biggest 'wow' factor of the day. That honour went to Van Niekerk, as the South African produced a performance that will live long in the memory.
Van Niekerk's incredible time of 43.03secs lowered his personal best by almost half a second and saw Johnson lose a world record he had set in 1999.
QUOTES OF THE DAY
"Somebody said I can become immortal. Two more medals to go and I can sign off. Immortal," - Bolt is not finished yet.
"Bolt told me in Jamaica, 'you will break the world record'. Tonight he said: 'I told you, you can do it'," - Van Niekerk reveals the 100m champion had motivated him to succeed.
"I knew the time was going to be fast but I didn't know it was going to be 43.0 fast," - LaShawn Merritt, bronze medallist in the men's 400m, reacts to Van Niekerk's astonishing display.
David Rudisha is arguably the biggest name in action on Monday, as he aims to defend the men's 800m title he won in such style at London 2012. Felix will be strongly fancied to triumph in the women's 400m.