Ian Thorpe predicted Aussie sprint king Kyle Chalmers would need a faster first 50m if he were to topple America's Caeleb Dressel because of the way he breathes - as the 23-year-old missed out on a gold medal by 0.06 seconds.
Chalmers, who came from nowhere to win gold as an 18-year-old at the 2016 Rio Olympics, was looking to become the first Aussie to repeat as the fastest man in water.
The country's most decorated Olympian Thorpe, who has nine medals including five gold, said before the race Chalmers' tendency to breathe on his right side would mean he wouldn't be able to see Dressel or the other swimmers for the last 50.