US star Regan Smith breaks McKeown's 100m backstroke WR

This world record was five years in the making for Regan Smith.

What an up-and-down journey it's been.

Bouncing back from a close-but-no-Olympics call in her first race, Smith set a world record in the women's 100m backstroke at the US swimming trials on Tuesday night.

The 22-year-old Minnesota native touched in 57.13 seconds, easily beating the mark of 57.33 set a year ago by Australia's Kaylee McKeown.

Smith was just 17 years old when she first set a world record in the 100 back at the 2019 world championships but she struggled to deal with the sudden, newfound fame, ceding dominance in the event to McKeown.

"A long time coming," Smith said.

"It's about time."

There was never any doubt about Smith's talent, but a lack of confidence was almost crippling at times.

She's been working with a sports psychologist since October, which helped turn things around from mental standpoint. Her coach, Bob Bowman, best known for his work with 23-time gold medallist Michael Phelps, took care of the physical side with a gruelling training regimen.

"This is incredibly rewarding," Smith said.

"When I was a teenager, I had not done much. There was no pressure on me. I was always the youngest ... I could go into it fearless."

Once she tasted success, it was hard to get back on top. She made the US team for the Tokyo Olympics, but finished third in the backstroke as McKeown took the gold.

"I've always had it physically, but I didn't have it mentally," Smith conceded.

"I just didn't have it up here," pointing towards her head.

Showing how much her confidence has grown, Smith bounced back emphatically after getting edged for a spot on the US team in the 100 butterfly, where she finished third behind Gretchen Walsh and Torri Huske.

Flipping to her back, Smith set the second world record of the trials, following Walsh's mark in the semi-finals of the 100 fly.

In the night's other final, Bobby Finke earned the right to defend the 800m freestyle gold he won in Tokyo with a time of seven minutes 44.22 seconds.

Finke had to work hard to get to the wall ahead of 18-year-old Luke Whitlock, who set a national age-group record at 7:45.19.

"I find I need pressure to do well, at least in my eyes," Finke said.

"So I feel like the more pressure I feel, then the more likely I am to do well. Happy with the time we got."

Whitlock splashed the water emphatically after going virtually stroke-for-stroke with the reigning Olympic champion, who swept the 800 and 1500 free in Tokyo.

He is expected to become the youngest male swimmer to make the US team since that guy named Phelps, who was 15 when he qualified for his first Olympics in Sydney in 2000.