Aaron Peirsol created the biggest buzz at the Indiana University Natatorium pool by reclaiming his world record in the 100 backstroke. The Olympic champion trailed Matt Grevers at 50 meters before pouring it on down the stretch to win in 51.94 seconds.
"That's a beautiful race," Peirsol said. "I knew I could do something special."
Peirsol became the first person to swim under 52 seconds in the event he has dominated. He has lowered the world record six times.
"The consistency is the thing I've always held myself high on," he said.
Peirsol's previous mark of 52.54 set in the Beijing Olympics was broken by Spain's Aschwin Wildeboer Faber on July 1. Faber swam 52.38 on the backstroke leg of the 400 medley relay at the Mediterranean Games.
Grevers finished second in 53.11, giving himself another crack at taking down Peirsol in the world championships in Rome.
Phelps held off David Walters in the closing meters of the 200 free and touched in 1 minute, 44.23 seconds. Walters pushed Phelps coming off the final turn, but settled for second in 1:44.95.
Ryan Lochte was third in 1:45.66. The eight-man field included the 800 freestyle relay team of Phelps, Lochte, Ricky Berens and Peter Vanderkaay that won at Beijing, one of the record eight gold medals won by Phelps.
Walters, who earned a gold in Beijing by swimming the relay heats, also qualified for Rome.
Phelps returned later to win the 200 fly in 1:52.76, well off his world record of 1:52.03 set in Beijing.
"I'm not happy about the 200 fly, but I think some of the things that happened are going to be helpful to me to swim faster," he said. "When I'm satisfied is when I'm doing a best time. I'm not used to not doing a best time when I shave and taper."
He was pushed in the next lane by Tyler Clary, who stayed close throughout and finished in 1:53.64.
"That was one of the greatest swims I've ever done," Clary said.
That wasn't the case for Katie Hoff.
Her second attempt to qualify for Rome ended in defeat again. She finished eighth and last in the 200 free, leaving her with only one more chance in the 100 free.
Dana Vollmer, a 2004 Olympian, won the race in 1:56.20.