INDIANAPOLIS — 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 finished strong to eclipse the mark of 55.48 set by Sweden’s Sarah Sjöström at the 2016 Rio de Janeiro Olympics.

She held her hand over her mouth as she looked at the scoreboard in disbelief, a “WR” beside her name.

The 27-year-old Walsh, a native of Nashville, Tennessee, who competes for the University of Virginia, will return for the finals Sunday night looking to claim a spot on her first Olympic team.