Phelps is back to form [GALLO/GETTY]

The 14-time Olympic gold medallist, who was suspended from swimming earlier this year, swam the two-lap final in 50.22 seconds at the Indiana University Natatorium.

He lowered Ian Crocker's mark of 50.40 set at the 2005 world championships in Montreal.

Phelps led at 50 metres with a split of 23.83, just three-tenths off world-record pace.

Known for his strong finishes, he pulled clear to beat Tyler McGill, who touched in 51.06. Aaron Peirsol was third in 51.30.

Home straight

"Crock had a ton more first 50 speed than I did. That's something I've really been working on,'' Phelps said.

"I've always been able to come home pretty strong. I finally got the front half a little bit faster. If I can get that even faster, I'll be in better shape.''

Phelps holds world records in the 100 and 200 flys, 200 and 400 individual medleys, and the 200 free.

Phelps had owned the 100 fly mark for a day at the 2003 worlds in Barcelona. But Crocker took it from him a day later, then lowered it twice more.

"I still remember the day at worlds when I broke it and the next day Crock broke it and Crock's had it ever since,'' he said.

"To finally be able to get it tonight means a lot.''

Last month, Phelps won the event at a meet in Montreal with a then-personal-best of 50.48.

Friendly competition

"Crock actually texted me after and wished me all the luck and telling me that was my record,'' he said.

"That meant a lot, from a competitor and a friend and a classy guy.

"We had amazing battles back and forth. Those are something I definitely miss.''

Crocker hasn't swum competitively since losing the 100 fly to Phelps at the Beijing Olympics, where Phelps won a record eight gold medals.

Phelps' victory gave him a spot in the event at the world championships this month in Rome. He already qualified in the 200 fly and 200 freestyle as he continues his transformation from swimming middle distances to sprints.