Indianapolis: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.
Neither of his 200m victories here was up to his exacting standards, and when he saw his time on Thursday Phelps ripped off his cap in celebration as spectators at the Indianapolis University Natatorium rose and cheered.
The fact that the record had stood for four years, and was held by his friend and intense rival Crocker, made the performance even more satisfying.
Phelps managed to seize the world record in 2003 - for a day - lowering the mark in the semi-finals of the World Championships in Barcelona before Crocker responded by reclaiming it in the final.
"I've wanted it ever since then," Phelps said.
Phelps, who bested Crocker in the 2004 Olympic final, was stung by Crocker in the 2005 World Championship final.
"I think this means a lot," Bowman said. "In the race where Ian broke that record, that's the worst that Michael has ever been beaten. That was an amazing record and that's why it has stood the test of time."
Phelps knew he was closing in on Crocker's mark when he swam 50.40 at a meeting in Montreal last month.
But he admitted that he was a little surprised to be swimming so fast after his lengthy post-Beijing break.
In addition, he returned to a new training regimen, which was promptly disrupted by a three-month competition ban over a tabloid photo of him with a marijuana pipe.
"I wouldn't have said when I got back into it that I'd be going faster than I did at the Olympics," Phelps said.
Beijing medallists Dara Torres and Rebecca Soni also booked World Championship berths, along with Nathan Adrian and Elizabeth Beisel.
Torres, 42 and battling a bum knee that will require surgery later this year to address a torn tendon and arthritis, won the 50m freestyle in 24.43.
It was well off her American record of 24.07, set in her three-silver campaign in Beijing. It will be Torres's first World Championships since 1986.
"It's a great feeling to be able to come out here and still race, but that time won't medal at the world championships," she said.
Adrian won the men's 50 free in 21.52, but he wasn't the fastest man in the pool.
That was Brazil's Olympic champion Cesar Cielo, who won the consolation final in 21.14 ahead of world record-holder Frederick Bousquet (21.36) of France.
Cielo had qualified for the championship final, but was bumped because only Americans are allowed to swim it. He and Bousquet notched the fastest times ever swum in America and would have finished one-two in the event.
Cullen Jones and Garrett Weber-Gale tied for second in 21.55 in the championship final and will duel again on Saturday for the second World Championship ticket.
Soni, the 200m breaststroke world record-holder, won the 100m breaststroke in an American record of 1:05.34. Beisel, 16, booked her first World Championship berth with a victory in the 400m individual medley in 4:36.31. Julia Smit was second.