BEIJING—Michael Phelps powered to the wall and whipped around to get his time, so eager to see another amazing set of numbers that he bumped his head on the end of the pool.

Not that he felt any pain.

With President Bush cheering him on, Phelps dominated his first event of the Beijing Olympics on Sunday morning, crushing his own world record and all hopes of his challengers with a mark of 4 minutes, 3.84 seconds in the 400-meter individual medley.

One down, seven to go in Phelps’ quest to break Mark Spitz’s record of seven gold medals.

“I’m not d...

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