Gretchen Walsh outdid herself and the rest of the world at the U.S. Olympic swimming trials Saturday when she shattered the women’s 100-meter butterfly world record in her semifinal race at Lucas Oil Stadium in Indianapolis.

She posted a 55.18 time in the two-lap event, breaking Swedish swimmer Sarah Sjöström’s 55.48 mark from 2016. 

“I didn’t think I was going to do it tonight,” Walsh said. “I just knew that I wanted to go a best time, and now, here I am, world record holder. It’s actually insane. 

“I think I was probably the most shocked of all the people I know. I think that they all had confidence in me. … I was absolutely in awe. Totally surprised.”

The 21-year-old University of Virginia star opened the day with an impressive 55.94 race in prelims to easily qualify for the semifinals, when she stormed out with another blistering performance. 

While Walsh dominated the second semifinal of the day, Regan Smith finished second at 55.92 to advance to Sunday’s final. Torri Huske won the first semifinal, posting a 55.79 time nearly breaking her own American record, and advanced as well. 

“It’s definitely been an emotional night,” Walsh said. “Luckily I have had experiences like this — obviously not breaking a world record but just trying to keep my emotions controlled. 

“I have a time where I'm going to put my phone down tonight and just let it be and hopefully get a good night's rest. But I warmed down, and I iced, and [stuck] to my recovery routine. So I'm hoping tomorrow night I just get a spot on the team because that's really what I came here to do.”

19-year-old Aaron Shackell wins men's 400 free

Aaron Shackell, 19, was the first U.S. swimmer to qualify for the Olympics at trials, winning the men’s 400-meter freestyle in 3:45.46. Aaron’s father, Nick, swam for Great Britain at the 1996 Atlanta Olympics. His siblings, twins Alex and Andrew, have also qualified for Olympic trials this week.

Katie Ledecky makes her fourth Olympic team

Katie Ledecky, who has won 10 Olympic medals since making her debut at the 2012 London Olympics, easily won the women's 400 freestyle to make her fourth Olympic team. She finished in 3:58.35.