The legendary Jamaican sprinter and the lightning-fast South African quarter-miler and newly-minted world record holder produced two of the greatest moments of the Rio Olympics in the space of 25 pulsating minutes.

In capturing a historic third straight Olympic 100m title, Bolt completed the first leg of his planned triple by again besting his controversial American rival Gatlin.

The Jamaican, who turns 30 on the day of the closing ceremony in Rio, was slow out of the blocks but had the race well in hand with 10 metres to run.

He clocked a winning time of 9.81 seconds ahead of Gatlin (9.89) and bronze medallist Andre de Grasse from Canada (9.91).

“I’m really happy but I expected to go faster,” said Bolt.

“I’m just happy that I won and that’s the key thing.

“After the semi-final I felt extremely good.

“I wanted to run faster but with the turnaround time, we normally have two hours, but we had one hour 20 minutes, it was challenging.

“I told you guys I was going to do it.

“Stay tuned, two more to go.”

Bolt is also the red-hot favourite to secure further golds in the men’s 200m and 4x100m relay later in the Rio Games, having also won all three Olympic sprints in 2008 and 2012.

The 34-year-old Gatlin is a highly divisive figure in the sport, having twice served doping bans.

The 2004 Olympic champion, who was heavily booed by the Rio crowd, has now finished second to Bolt in the 100m at the 2012 and 2016 Olympics and the two most recent world championships.

Gatlin looked to have finally got Bolt’s measure at the 2015 world titles in Beijing, only for the peerless Jamaican to dig deep in the 100m final and edge home by one hundredth of a second.

This time it wasn’t even particularly close.

The men’s 400m was an even more one-sided affair with Van Niekerk setting a remarkable pace in the outside lane.

His time of 43.03 seconds stripped 0.15 off the world record set by Johnson back in 1999.

Johnson was in the Olympic stadium on Sunday night calling the action for the BBC.

“He took it out so quick. I have never seen anything from 200 to 400 like that,” said Johnson.

“That was a massacre from Wayde van Niekerk. He just put those guys away.”

Defending champion Kirani James from Grenada was second in 43.76 and American LaShawn Merritt was third in 43.85 in a stunning race where four of the top six finishers set personal bests.

“I believed I could get the world record,” said Van Niekerk.

“I’ve dreamed of this medal since forever. I am blessed.”

The other gold medal decided on Sunday went to Caterine Ibarguen from Colombia in the women’s triple jump with 15.17m.

-AAP