Phelps broke his own 200-meter butterfly record Saturday, winning in 1 minute, 53.71 seconds, nine hundredths of a second faster than his time from August 2006. He beat Tamas Kerekjarto of Hungary by more than six seconds.
"I didn't expect that, that's for sure," he said after the race. "Coming in tonight, I wanted to go 1:55, 1:54 the fastest. Right now, I guess things are going well."
Phelps, who earned six gold medals and two bronzes in the 2004 Olympics, plans to compete in 17 events in Melbourne, defying most of his peers' choices to specialize in one or two events. He will race in two more events Sunday and three on Monday.
On Friday, Phelps spoke about capitalizing on his notoriety as America's most recognizable swimmer _ and his refusal to specialize.
"I know it's challenging for me to swim so many events back-to-back-to-back," he said. "But it's something that I've wanted to do for quite some time. It's something I think will help change the sport of swimming."
Fellow Olympian Natalie Coughlin easily won her only race Saturday with a time of 53.95 in the 100-meter freestyle, just 12 hundredths of a second off her personal best.
"It was a fun race for me," she said. "This is my first long course meet in a really long time and a tune up for the world championships. I'm glad how it turned out."
In the men's 200-meter backstroke, two-time Olympian and world-record holder Aaron Peirsol won with a time of 1:56.27 seconds.
A total of 19 Olympians are participating in the event, the first of its kind at the University of Missouri's new pool.
Despite the high-profile field, the meet's public address announcer had to repeatedly urge the crowd _ many attending their first elite swim meet _ to cheer and holler for the swimmers.
Once Phelps emerged, that reticence was quickly gone, with fans and other competitors alike captivated by the ease of his dominance.
"It's incredible," said Coughlin, who missed the record-breaking performance because she was taking a drug test. "I'm sorry I missed it. I'm sure he'll do it again next month."