Australian teen Kyle Chalmers has overshadowed compatriot Cameron McEvoy to win gold in the 100m freestyle final.
The 18-year-old stormed home to touch the wall first, with McEvoy finishing seventh.
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DREAM: Chalmers' dream to play AFL
It is Australia's first men's 100m freestyle victory since Michael Wenden in Mexico City in 1968.
He is Australia's fourth 100m freestyle Olympic champion, following Wenden, Jon Hendriks (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 still sinking in", he said post-race. "I faded towards the end and I was a bit worried, but very happy now.
"Unbelievable, I'm only 18 so it was pretty daunting but I knew I had to stick to my guns."
The win sparked some incredible reactions from Chalmers' classmates at Emmanuel College, as well as his teammates backstage:
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 Adrian (47.85) claimed the silver and bronze medals.