The 24-year-old powered to the wall in a new Olympic record time of 47.02sec
US star Caeleb Dressel said he was never worried as he blazed to his first individual Olympic gold medal in the men's 100m freestyle final on Thursday, adding to his back-to-back world titles.
The 24-year-old powered to the wall in a new Olympic record time of 47.02sec to dethrone charging Australian defending champion Kyle Chalmers, who came second (47.08). Russia's Kliment Kolesnikov took the bronze in 47.44.
"It's been a really tough year, really hard. I'm really happy," he said in tears as he was connected via video link to his wife and family back home.
Dressel missed out on the individual medals at Rio in 2016, but he has since exploded, winning an incredible 13 titles over the past two world championships.
Despite the nailbiting finish, he said he was never concerned.
"I wasn't worried about anything," he said. "During the race there's only so much you can do. Whatever's gonna happen is going to happen.
"I stuck to my race plan -- if it got me first, OK, if it got me second OK. I wouldn't change a thing."
Dressel went to the turn in front but had to dig deep to hold off Chalmers, needing to smash the previous Olympic record of 47.05 held by Australia's Eamon Sullivan since 2008.
It was Dressel's second gold in Tokyo after spearheading the United States to the 4x100m relay title on Monday. He will also race the 50m freestyle and 100m butterfly, and could feature in two other relays.
But it was his first individual title at an Olympics after two relay golds in Rio, a feat he was proud to achieve.
"I didn't want to admit it but now I did it I can admit it, it's a lot different," he said.
"You can't rely on anyone else. It's just you in the water, there's no one there to bail you out. It's tough. It's really tough. So I'm happy to actually do it."
Chalmers said he was disappointed not to successfully defend his title, but did all he could.
"It is a bit bittersweet. To get second is amazing, and to back it up with gold in Rio and the five-year journey, which has been really challenging and to get silver is special," he said.
"But to be so close -- it does hit home a little bit."
Chalmers had shoulder surgery last year and likely wouldn't have competed if the Olympics had not been postponed for a year due to the pandenic.
He has also battled ankle and back issues and undergone three surgeries in recent years for a non-life-threatening condition that makes his heart beat abnormally fast.
"Everyone has challenges but to stand up and set an equal best time in an Olympic final when it counts most with all the pressure and expectation on me, it is special," he added.