Caeleb Dressel, less than nine hours removed from an Olympic record victory in the men's 100m freestyle, equaled another Olympic record with a 50.39 swim in his 100m butterfly preliminary heat.
The 100 fly is considered Dressel's strongest event. At the 2019 World Championships, he broke Michael Phelps' decade-old world record of 49.82, lowering the mark to 49.50.
Dressel, already a two-time gold medalist at the Tokyo Games, is the prohibitive favorite in the event and still has both the semifinals and final to potentially challenge his own world record.
Friday's semifinal round may be Dressel's best chance at testing the mark, as the Saturday final falls within the same session as two other events in which Dressel is expected to race: the 50m freestyle semifinals and the mixed 4x100m medley relay final.