Park, who floated his prelim swim, a very easy-looking effort, landing himself in lane one for the final...not the ideal stretch of water to race in. He shot-out to an early lead, backed off the gas a little in the middle of the race, and then dropped the hammer for the win.
The victory must have felt sweet after he failed to make the 400 free world final in 2009.
Park became a household name in the global swimming community when he won Olympic gold in Beijing in the 400 free at the tender age of 19.
Sun Yang, China's star and the favorite to win the race (after posting a 3:41 at Chinese Nationals earlier this year) was second with a 3:43.24.
Paul Biedermann of Germany (the 2009 World Champ in this event, 4:40, aided by a hi-tech suit) took the bronze in 3:44.14.