Kyle Chalmers pulled off a stunning late surge to snatch a breakthrough gold medal in the men's 100 metre freestyle at Rio 2016.
The Australian qualified with the second-fastest time but was lagging second from last at the turn in the sprint race.
An anticipated battle between Chalmers and pre-race favourite Nathan Adrian - the reigning Olympic champion - failed to materialise as the American rarely threatened the lead and finished third.
Chalmers' closing speed in the final strokes was astonishing, the 18-year-old just edging out Belgium's Pieter Timmers with a time of 47.58 seconds.
"It's definitely still sinking in," Chalmers told Channel 7.
"It was a good race. I faded towards the end, was a bit worried at the finish but I've got to be very happy with that.
"I'm only 18, Nathan's 10 years older so to be next to him was daunting but I had to stick to my guns."
Chalmers will now turn his attention to surgery to fix arrhythmia after an operation last year could not correct an irregular heartbeat.
His compatriot Cameron McEvoy, who entered the Games with the third-fastest time ever in the 100 freestyle and the fastest in the textile era, finished a disappointing seventh.