Rio Olympics: Kyle Chalmers claims 100m freestyle gold for Australia

Australian swimmer Kyle Chalmers claimed a shock Olympic 100m freestyle gold medal on Wednesday night.

The 18-year-old became the first Australian since Michael Wenden in 1968 to win the Olympic event, while compatriot and pre-race fancy Cameron McEvoy finished seventh in 48.12.

Chalmers is Australia's fourth 100m freestyle Olympic champion, following Wenden, Jon Hendricks (1956) and John Devitt (1960).

Chalmers produced a stunning last lap to overtake the field - he turned in seventh place.

The South Australian entered the final in great form, setting two junior world records on his way to becoming the second fastest qualifier for the final - and then setting another in the medal race.

Few predicted he would upset defending American defending Olympic champion Nathan Adrian and world No.1-ranked teammate McEvoy.

"It's unbelievable, I'm only 18," Chalmers told the Seven Network.

"Nathan's 10 years older than me and already an Olympic champion so being next to him was pretty daunting for me but I knew I had to stick to my guns."

McEvoy had arrived at Rio as the red-hot favourite after clocking 47.04 seconds at April's Rio trials - the third fastest of all time and quickest outside the 2008-09 supersuit era.

Yet McEvoy became the latest Australian Olympic 100m fancy to walk away empty handed.

Eamon Sullivan (2008) and James Magnussen (2012) had also gone into the last two Olympics as the overwhelming 100m gold medal fancy, only to leave broken hearted.

Belgian Pieter Timmers (47.80) and American Nathan Adrian (47.85) claimed the silver and bronze medals.

"I've had a lot of people give me some good advice. I like to think of myself as country boy... and country people are pretty relaxed the whole time," Chalmers said.