INDIANAPOLIS (AP) — Gretchen Walsh set a world record in the women’s 100-meter butterfly Saturday night, posting a time of 55.18 seconds in a semifinal heat at the U.S. Olympic swimming trials.

Walsh was more than a half-second under world-record pace at the turn and held on to eclipse the mark of 55.48 set by Sweden’s Sarah Sjöström at the 2016 Rio de Janeiro Olympics.

“I definitely was feeling it,” said Walsh, who considers herself a stronger swimmer in the short-course pool. “I thought I was dying. I didn’t know I was going that fast and, apparently, I took it out too fast.”

Not to worry. Walsh held her left hand over her mouth as she looked at the scoreboard in disbelief, a “WR” beside her name.

“There has been a little bit of a buzz out there,” she said. “I think going into tonight, like I knew it would take a (55) point-4 or I guess point-5, but I didn’t think I was going to do it tonight. I just knew I wanted to go a fast time and now here I am — a world-record holder.”

The 21-year-old Walsh, a native of Nashville, Tennessee, who competes for the University of Virginia, still has some work to do to claim a spot on her first Olympic team.

In the final Sunday night, she will face a strong field that includes Torri Huske, Regan Smith and Claire Curzan — all of them medalists from the Tokyo Games.

But Walsh feels she can go even faster.

“I still have room to grow in that race,” she said.