Michael Phelps broke the 100m butterfly world record, evidence that his post-Olympic transition is right on track.
Phelps, winner of eight gold medals at the Beijing Games last August, won in 50.22sec, slicing 18-hundredths of a second off the previous record of 50.40 set by compatriot Ian Crocker at the 2005 World Championships in Montreal.
"It was big," Phelps said of the achievement. "This is something I really wanted to accomplish."
Thursday's performance took Phelps's current tally of individual world records to five, to go with three relay world records.
Since 2001, when he set his first world record in the 200m butterfly, Phelps has set at least one world record in all but one year - 2005.
That was another post-Olympic year, and Phelps's coach, Bob Bowman, said he hadn't been sure that Phelps would lower a world mark this season as he retools his training to tackle shorter events.
"I was hoping he'd be on the World Championship team," Bowman said. "I wasn't sure he'd break a world record this year."
In fact, Phelps has now qualified for three events at the upcoming World Championships in Rome, after victories in the 200m free and 200m butterfly on Wednesday. He is slated to race the 100m freestyle on Friday.