CHARLOTTE, N.C. -- Michael Phelps is not unbeatable.
Not when he's going against Aaron Peirsol.
The world-record holder and two-time Olympic champion handed Phelps his first defeat in almost a year, winning the 100-meter backstroke at the Charlotte UltraSwim on Saturday night.
Wearing his new Arena suit, Peirsol got off to a strong start and touched in 53.32 seconds. Phelps was trailing by more than a half-second at the turn and had no chance to make that up against one of the world's greatest backstrokers, taking second in 53.79.
Phelps will remember this one.
"No matter who I'm racing, I hate to lose," he said. "Aaron and I have had a number of battles back and forth. ... That's the fun part about racing Aaron -- you know he's always going be there. He's a racer. He's a competitor. He's someone I like to race."
Phelps' last defeat in a final? Exactly 364 days ago, when Peirsol beat him in the 200 backstroke at Santa Clara, Calif., during the run-up to the Olympics, according to USA Swimming.
Phelps didn't swim the backstroke in Beijing -- it didn't fit into the schedule that produced a record eight gold medals and made him the winningest Olympian ever. But he's changing things up as he looks ahead to this summer's world championships and the 2012 London Games.
The 100 backstroke is one of his main targets.
Bring it on, Peirsol said.
"By no means is anybody giving anything to anybody," said Peirsol, who set a world record in the 100 back while winning his second straight Olympic gold in the event at Beijing. "I definitely wanted to win that race."
Phelps is competing in five events at Charlotte -- his first meet since Beijing -- but only two were on his Olympic program. He won them both on Friday night, the 200 freestyle and 100 fly.
He swam the 50 free during the Saturday morning prelims and posted the eighth-fastest time, but that was merely a chance to test out the new straight-arm stroke he'll use in his final event, the 100 free on Sunday. Phelps scratched from the 50 final, which was won by world-record holder Frederick Bousquet of France.
There's still some work to do in the 100 back, not to mention some stout competition. Ryan Lochte, the Olympic champion in the 200 back, finished fourth Saturday night -- not bad considering he was wearing an old-fashioned Speedo brief instead of one of the high-tech suits.
Phelps' coach ripped off a lengthy to-do list when they get back to Baltimore.
"There's probably three or four things in that race he can do better," Bob Bowman said. "His start wasn't very good; he came up really bad from his start. His turn was not exactly where it should be. And he didn't have any legs at the end. That's just conditioning."
Still, Phelps tried to put the loss in perspective. He's coming off a nine-month layoff that was by far the longest of his career. He had intended to come back sooner, but had to serve a three-month suspension imposed by USA Swimming after a British tabloid published a photo of him using a marijuana pipe.
The suspension ended May 5.
Now it's time to chase down Peirsol.
"When Michael gets beat, he remembers the race more," Bowman said. "When I say, 'Let's do some kicking to help with the 100 back,' it'll have more credence."
Phelps was done when he made the turn in 26.64 -- putting him 0.62 behind Peirsol.
"If he's going to race Aaron, he's got to be on even terms one time and see what happens," Bowman said. "You don't come back on someone who's the best finisher ever. You have to push him a little bit."
Peirsol was surprised by his big lead at the flip.
"I couldn't see him, so I thought he was probably really far ahead of me," Peirsol said. "When he wasn't, that made things a little easier."
Still, this has the makings of a very juicy rivalry. Phelps said he's not planning to hang a picture of Peirsol next to his bed as he once did with Ian Crocker when those two were battling in the 100 butterfly.
Not yet, anyway.
"This is going to come back with me," Phelps said of the loss. "It doesn't matter what stroke it is or what event it is, I don't like to lose. Aaron has got the upper hand on me in pretty much all of our races."
Though she's been overshadowed by Phelps' return, 17-year-old high schooler Dagny Knutson has actually won more events in Charlotte than the star attraction.
Knutson, who trains without benefit of a team or world-class facilities in her native North Dakota, picked up her third gold medal of the weekend with another win over Olympian Katie Hoff, this time in the 400 freestyle. Knutson won with a personal-best time of 4 minutes, 9.60 seconds.
Hoff, who changed coaches after a disappointing performance in Beijing, has yet to recapture the form that made her one of the most hyped swimmers not named Phelps going into the Olympics. She was edged at the wall in 4:09.72, after also losing to Knutson in the 200 free.
The North Dakotan's other win came in the 400 individual medley.
Bousquet only entered the meet on Wednesday, less than a month after becoming the first swimmer to break the 21-second barrier in the 50 free.
He failed to match his 20.94 from the French national championship, but turned in the fastest time ever posted in the U.S. -- 21.33. Olympian Cullen Jones, who trains in Charlotte, was second in 21.92.
Bousquet, a former college star at Auburn, is eager to take the record even lower, though his main goal is winning a world championship in Rome this summer.
"I can shoot for sub-20 one day," he said. "I'm trying not to put any limit on it. But right now, it's more a matter of winning the race than going fast. I really want to win the 50 at the world championships. I know it's going to be very hard. These guys are bringing it big time."