INDIANAPOLIS — Ian Crocker spent months training for another chance to beat Michael Phelps in the 100 butterfly.

His hopes vanished before the race even started.

The rivalry between two of America's best swimmers at the national championships ended when a strobe flash inadvertently went off just before the race started.

Crocker reacted with a flinch, and as the Indianapolis fans gasped, the world-record holder already knew his fate — disqualification.

"I heard the crowd when it happened, and I was pretty sure if they had seen the flinch, the officials had seen it, too," Crocker said. "That's their job."

But the fans still got to watch the highly anticipated race, and Phelps won it anyway, pulling away in the final 25 meters with a time of 51.39 seconds to break his own long-course record at the national championships.

Crocker, whose time was quickly scrubbed from the scoreboard and replaced by the dreaded disqualification symbol, said he swam a 51.6.

The loss was tough enough, but the distracting light was even more disconcerting to Crocker.

"It's one of those things and I guess it's a learning experience for myself, and, hopefully for U.S. swimming and people like that, too," Crocker said. "I've never had that happen to myself and I've never known it to happen to anyone else."

Jamie Fabos, a spokeswoman for USA Swimming, said officials were trying to determine whose flash went off. If they do, the offending news organization's strobe will be revoked for the rest of the meet, Fabos said.

Both Phelps and Crocker acknowledged there is usually a light flash, signaling the start of the race. To avoid getting confused, Phelps keeps his head down.

"I don't go by the flash, I go by the sound," Phelps said. "You could see it very clearly on the replay that the strobe went off."