USA's Caeleb Dressel secured gold in the men's 100m butterfly, breaking his own world record with a time of 49.45 seconds.
Hungary's Kristof Milak broke the European record in silver position, 0.23 seconds behind Dressel (49.68), while Switzerland's Noe Pointi picked up the nation's third ever medal in swimming for bronze (50.74).
Dressel got off to a fast start, leading 0.65 seconds ahead of Milak and ROC's Andrei Minakov at the first turn.
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Marathon Swimming - Men's 10km - Tokyo 2020 - Olympic Highlights
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And the 24-year-old Floridian, who has already won gold in the 4x100m freestyle relay and 100m freestyle at this Games, burst into a considerable lead in the second 50m and was motoring ahead of the world record line.
Milak had a late burst in the final 25m, but Dressel would not be caught as the American registered the new record time.
"A couple more metres and I think Milak would have had that," Lizzie Simmonds said on Eurosport commentary.
"Dressel was leading all the way there. He had an awful finish, he glided miles into the wall and I wondered for a second if Milak had that.
"I don't think we expected it to be that close, but a very good swim from Milak and fabulous to see the second world record go in an individual event at this Olympic games."
Australia's Kaylee McKeown won her second gold medal at Tokyo 2020, this time in the women's 200m backstroke final with a time of 2:04.68.
Canada's Kylie Masse took silver (2:05.42) and fellow Australian Emily Seebohm finished in bronze position (2:06.17).
McKeown has become the seventh woman to win both the 100m and 200m backstroke in Olympic history.
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