Kalisz took gold in the 400 meter individual medley on Sunday, beating U.S. teammate Jay Litherland by 0.86 seconds.
For the first time at this year's Games, an American stands atop the podium.
Chase Kalisz won gold at the 400 meter individual medley on Sunday, capturing the first gold medal for Team USA at the Tokyo Olympics. Kalisz won silver in the event at the 2016 Games in Rio, and Sunday's win marks his first career gold at the Olympics.
American Jay Litherland took silver, finishing 0.86 seconds behind Kalisz. Australia's Brendan Smith came in third.
An American had won gold in this event five straight times from 1996 to 2012, with the gold medals dispersed across three different swimmers: Tom Dolan (1996 and 2000), Michael Phelps (2004 and 2008) and Ryan Lochte (2012). Japan's Kosuke Hagino took gold in 2016.
Kalisz, 27, is from Bel Air, Md., and swam collegiately at the University of Georgia, where he was a three-time NCAA champion.
"It means the world," Kalisz said on the NBC broadcast after his race, per Christine Brennan of USA Today. "This is the last thing that I really wanted to accomplish in my swimming career. It was something that was a dream of mine since as long as I could remember."
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