INDIANAPOLIS — Gretchen Walsh announced herself as the breakout swimming star of the 2024 Olympics before she even qualified for them.

Walsh smashed the world record in the women’s 100-meter butterfly semifinals here on Saturday night, the opening night of U.S. trials.

Her 55.18 took down Swedish sprinter Sarah Sjöström’s 55.48, which had stood as the best-ever mark since the 2016 Olympics.

It was the first time a world record has fallen at U.S. Olympic trials since Michael Phelps set a new best in the 200 individual medley in 2008, according to NBC.

Walsh will now look to make her first Olympic team Sunday night in the 100 fly final. But no matter the result, she said, “I'm gonna be at peace with the fact that I've already accomplished so much at this meet, more than I ever thought I would.”

Walsh, a University of Virginia junior who wrote and rewrote NCAA record books this past season, entered trials as a short-course star but a long-course question mark.

“Everyone always says I’m just a bathtub swimmer,” she said in November. She sped to NCAA acclaim in 25-yard pools, which accentuate her underwater excellence; but 50-meter pools — the international standard, where swimmers must spend twice as much of any race on top of the water — are “an entirely different beast for me,” she acknowledged Saturday.

Over the past few seasons, though, after missing the 2021 Olympic team as a teen, she conquered the beast. After shattering records at NCAA championships, her Virginia group “flipped the training program on its head.” The long-course-focused regimen was “a little scary for me at first,” she admitted last month. “Because I really do just rely on my underwaters when I do short-course.” But she worked to lengthen her stroke and up her efficiency. “I feel like I've definitely improved with my actual swimming,” she said.

“I've spent a lot of training focusing on the 100 fly specifically,” she added here on Saturday.

“So, to have it translate into the real pool, some would say, really goes to show that [training] is paying off.”

Her coach, Todd DeSorbo, would tell her that a world record was coming; that it was “just a matter of time.”

The time arrived, though, sooner than anyone expected — including Walsh herself.

“I did not know that I was gonna go 55.1 and break the world record,” Walsh said. “It doesn't feel real.”

To even hear her name in the same sentence as Sjöström — a now-30-year-old legend who set or lowered the 100 fly record five times beginning in 2009 — “is insane,” Walsh said.

Her mind was still racing hours after she touched the wall. "It's definitely an emotional night," she said. Her next challenge, she knew, would be to slow herself down; to stick to her recovery routine; to warm down, and ice, and unwind.

“I'm gonna put my phone down tonight, and just let it be, and hopefully get a good night's rest,” she said. Because, well, she is still not an Olympian. And despite the world record, she isn’t a lock to become one.

Torri Huske, the previous American record holder, and Regan Smith, a 2021 Olympic medalist, will push her in Sunday's 100 fly final. Only two of the three can make Team USA in this uber-competitive event. Huske was also under world-record pace at the 50-meter mark in Saturday’s first semifinal heat; she finished in 55.79. Smith went 55.92, within touching distance.

So Walsh will need to recharge for another battle. Her hope, she said, is to "just get a spot on the team ... because that's really what I came here to do."