Australia has a new Olympic hero -- and his name is Kyle Chalmers.

The 18-year-old stunned the field in the men's 100-meters freestyle final to claim gold and become the first Australian to win the event since Mike Wenden in 1968.

Chalmers, who had already won bronze in the 4x100-meter freestyle relay, edged out Belgium's Pieter Timmers and defending champion Nathan Arnold of the US.

The teenager was seventh on the turn but powered through the final length to claim a shock victory.

"It's definitely still sinking in that I've actually won," Chalmers told reporters after the race. "I was a bit worried that I glided for a bit too long at the finish but very happy with that.

"It's unbelievable, I mean, I'm only 18. Nathan [Adrian] is 10 years older than me and he's the reigning Olympic champion so being next to him was pretty daunting for me but I knew I had to stick to my guns."