Regan Smith, from Lakeville, Minnesota, eclipsed the world record of 57.33 set by Kaylee McKeown in Budapest in October 2023.

"It was part of the plan," Smith said of reclaiming the record she held in 2019.

She signalled her intentions by lowering the American record to 57.47 in the semi-finals and, with Katharine Berkoff pushing her all the way, made a final push to shave two-tenths of a second off McKeown's mark.

"I'm so proud of myself," said Smith, who won two silvers and a bronze at Tokyo 2020. "The backstroke is hard for me sometimes, but to fight like that and get it back means so much."

Berkoff finished second in 57.91 to complete a strong double for the USA in this event in Paris, where McKeown will remain a formidable rival. She clocked 57.41 at the Australian trials last week.

Smith, who missed out on a place in Paris in the 100m butterfly behind world record holder Gretchen Walsh and Torri Huske, has two events left this week at the Lukas Oil Stadium, the cavernous 32,000-seat home of the NFL's Indianapolis Colts, twice the size of the venue for the swimmers at Paris 2024.

"We're going to take a few minutes to be really proud of what I've achieved and then get back to work," said the 22-year-old swimmer. "I have more things I want to achieve this week."

Bobby Finke, double long-course freestyle gold medallist in Tokyo, secured his title defence in the 800m with a win in 7:44.22, with teenager Luke Whitlock second in 7:45.19.

Meanwhile, Caeleb Dressel qualified safely for the men's 100m freestyle final with the third-fastest time in the semi-finals. The American, who won five medals at Tokyo 2020, including the 50m and 100m freestyle and the 100m butterfly, ends the uncertainty surrounding his performances after taking a nine-month break from the sport and failing to qualify for the 2023 World Championships.

Chris Guiliano, already booked for Paris after finishing second to Luke Hobson in the 200m freestyle, led the semi-finals in 47.25 seconds.

In the second semi-final, 21-year-old Jack Alexy overtook Dressel to win in 47.33, with Dressel touching in 47.53.

It was Dressel's fastest time in two years and he was beaming as he looked at the scoreboard and shook Alexy's hand over the lane rope.

Simone Manuel, who won gold in the women's 100m freestyle in Rio de Janeiro in 2016 but failed to reach the final at the Tokyo trials as she struggled with the effects of overtraining syndrome, won her semi-final in 53.16 seconds to enter Wednesday's final with the second-fastest time behind Huske.

Huske clocked a personal best of 52.90 to secure her second ticket to Paris.

These trials show that world swimming remains in full swing in the Olympic build-up. Smith's record joins those of Ariarne Titmus in the 200m freestyle, Gretchen Walsh in the 100m butterfly and Summer McIntosh at these US trials.