Olympic swimming gold medalist Michael Phelps, left, shakes hands with Aaron Peirsol after Peirsol won the 100-meter backstroke Saturday night in Charlotte, N.C.

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.

“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 swimming five events in 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.