Quincy Wilson became America's youngest-ever track Olympian in the men's 4 x 400-metre relay first round - but left his senior colleagues scrambling after a baptism of fire. 

The 16-year-old left the United States second-to-last in the race after running a first leg of 47.3 seconds. 

That left Vernon Norwood, Bryce Deadmon, and Christopher Bailey needing to make up ground to qualify for the final.

They did just that, but it was only on the last leg that Bailey snuck into the top three to ensure safe passage to the grand stage. 

Botswana and Great Britain finished aheasd of the States as Thursday night's 200m gold medalist Letsile Tebogo ran an extraordinary leg.  

Wilson had run a personal best on July 19 when he ran 44.20s at the Holloway Pro Classic in Gainesville. 

That race on the even of the Olympics improved his under-18s world record and proved his potential on the big stage.

Ahead of his debut, he said: 'When I got the call, I was like, I was ecstatic.

'I started running around the house. It was just a moment for me because everybody dreams about going to the Olympics as a young kid.'

His mother, Monique, remembers having to chase him around from when he was 10 months old. 

'It was a lot of energy, jumping and running around at a very young age. And [real] running, like he wanted to be all over the place. I could tell that he was going to be something,' she told The Guardian. 

Wilson said: 'It’s been extremely hard to get here, but at the end of the day, I know that the hard work is why I’m in the position that I am in right now.

'And I think one of my special abilities is being able to know in a workout that the hard work that I’m doing is going to pay off – if not this week, next week, or next year, I know that at some way, or somehow I learned a lesson on the track or in life.'