China's Sun Yang beat 2008 Olympic champion Park Tae-hwan of South Korea to win the men's 400-meter freestyle on Saturday night.
Sun broke Ian Thorpe's Olympic record with a time of 3 minutes, 40.14 seconds, touching nearly two seconds before Park, who had been reinstated for the final after his country successfully protested a disqualification in the morning heats.
American Peter Vanderkaay won the bronze medal and teammate Conor Dwyer finished fifth.
It was an up-and-down day for Park, who was DQ'd in the morning for a false start only to learn hours later that he was in the final after a ruling by FINA.
"I felt bad. I was almost heartbroken, but I decided I would not think about it," said Park. "There was a problem but now it is solved."
Ryan Cochrane, the Canadian record holder in the 400, was bumped from the eighth and final qualifying spot when Park was shifted back in.
Earlier, Cochrane had written on Twitter: "Snuck right in that final for tonight! I'm excited to see how it all pans out..." before adding, "anything can happen at the olympics!"
Vanderkaay collected his fourth Olympic medal and second bronze. The other two are relay golds from Athens and Beijing.