South Australian teenager Kyle Chalmers is the toast of the nation after winning gold in the men’s 100m freestyle at the Olympic Games.

The 18-year-old looked in trouble at the turn on Thursday, but stormed home to claim a stunning and unexpected victory in 47.58 seconds.

Chalmers is the first Australian to win the event since Michael Wenden in 1968, and his triumph was a form of revenge for the green-and-gold after James Magnussen cruelly missed out by 1/100th of a second in 2012.

Chalmers saw off Belgian Peter Timmers (47.80secs) and Magnussen’s London conqueror, American Nathan Adrian (47.85secs) for victory, while pre-race favourite and fellow Australian Cameron McEvoy (48.12secs) could only manage seventh.

Watch the final stages below

https://twitter.com/7olympics/status/763557539510308864

“It’s definitely still sinking in that I have actually won. It was a good race,” a relaxed Chalmers told the Seven Network afterwards.

“It’s unbelievable. I’m only 18.

“Nathan [Adrian] is 10 years older than me, already being an Olympic champion, [so him] being next to me was daunting.

“I had to stick to my guns … he was a body length in front of me, once I came off the wall [in the second 50m] I had to build and get to the wall first, which I managed to do. I’m very happy.

McEvoy (L) congratulates Chalmers after the race. Photo: Getty

“It’s amazing having my parents here – I’m so grateful they made the journey over.

“It was a very expensive thing for them to come over here but I’m very, very grateful to be able to look up in the crowd and see my parents after a race like that.”

See the reaction at Chalmers’ school below

Could play that again n again 😊 RT @Timmy_morgs: PANDEMONIUM!!! GOLD FOR CHALMERS pic.twitter.com/DhhduSiRbk

— Michelle Prak (@Prakky) August 11, 2016

Chalmers attributed his cool and calm manner to his upbringing in South Australia.

“I like to think of myself as a country boy – that’s where I grew up,” he added.

“Country people are really relaxed the whole time … I feel like I’ve got that.

“As massive thanks to everyone – the amount of support I’ve got since swimming the relay is incredible. I love the support, thanks very much, I hope you enjoyed watching tonight.”

Chalmers was relaxed before the race. Photo: Getty

A humble McEvoy acknowledged he did not perform at his best but was quick to put the spotlight back onto Chalmers.

“Not the best,” McEvoy told the Seven Network.

“But enough about me. Kyle has come in, he’s done half a second PB [personal best] on top of PB at the trials, he just turned 18 and is an Olympic champion – that’s bloody wonderful.”

Groves wins silver

Just before Chalmers’ final, Madeline Groves was pipped by three hundredths of a second in the women’s 200m butterfly decider.

The Australian finished strongly but was just edged by Spain’s Mireia Belmonte Garcia, who won in two minutes and 4.85 seconds.

Groves (2:04.88secs) was well ahead of the third-placed swimmer, Japan’s Natsumi Hoshi (2:05.20secs).

Groves waves to the crowd after her medal. Photo: Getty

The Brisbane product was delighted to have produced a personal best in her final, though, and to finish with a medal.

“It feels amazing,” Groves told the Seven Network.

“I’ve had an awesome time – I’m so happy.

“I’ve had so much fun … I have so much respect for Mireia, I knew she would be there in the last 100.

“I was looking forward to the race and the challenging. I left everything in the pool.

“I gave everything I had, I’m really happy.

“That’s a personal best – it’s a bloody awesome time. I could have come last in that race, it doesn’t matter – I’m happy.”

Another silver

Australia also won a silver in the women’s 4x200m freestyle relay.

The Aussies led after three legs of the race but Tamsin Cook had no answer for 19-year-old American star Katie Ledecky in the final stages.

Ledecky – who has now won four gold medals – helped the US home in a time of seven minutes and 43.03 seconds. Australia finished in seven minutes and 44.87 seconds.

Cook told Seven: “I’m so happy for us.

“I had to stick to my race plan because if I try to go out with Katie Ledecky [and try and match her], it would have [been] a different result.”