Kalisz snares America's first gold of Tokyo Games

An emotional Chase Kalisz claimed the United States' first gold medal of the Tokyo Olympics with victory in the men's 400m individual medley on Sunday, slaying his demons from the 2016 Rio Games in the process.

Kalisz led by a body-length after 300 metres and stormed home in 4mins 09.42secs ahead of second-placed compatriot Jay Litherland (4:10.28) and Australia's Brendon Smith in third (4:10.38).

He said the win made up for the disappointment of finishing runner-up in Rio, when he felt his silver tarnished the legacy of US greats such as Michael Phelps in the event.

"I really do feel I kind of let the US down in 2016, even though I swam a lot faster than I did here -- this was my redemption story, it certainly wasn't an easy path," he said.

"It was tough last year with the Olympics getting pulled out from under us and having so much uncertainty around whether it was even going to happen -- it was five years of preparation  for this one moment."

Kalisz's gold was the first of six US medals on the first day of finals in the pool, with his teammates claiming two silver and three bronze, and the first won by the Americans at the Tokyo Games overall.

"That's really cool. I hope I can motivate the rest of my teammates," he said.

"We have a great team here and I think we're ready for more kick-ass performances... that's what the Olympics is all about."

France's Leon Marchand set off at a cracking pace and turned first after the butterfly leg, but Kalisz was always in touch and after a strong backstroke swim took charge in the breaststroke.

It turned into a mad scramble for the minor placings with Litherland just bettering Smith.

Kalisz said the race left him totally spent.

"That was a special type of pain, that one definitely hurt," he said. "I vowed that I was going to make it hurt as much as possible and give my absolute best to accomplish this."

Kalisz, 27, raised the prospect of retirement after finally fulfilling his childhood dream.

"This is the last thing I really wanted to accomplish in my swimming career," he said.

"It was a dream of mine since as long as I can remember. I can't believe it. I really can't believe it."

Kalisz took silver behind Kosuke Hagino at Rio in 2016, but the Japanese opted out of the event on home soil to focus on the 200m medley.

Rio bronze medallist and world champion Daiya Seto failed to qualify for the final.