"It's going to come back with me. I don't like to lose," said Phelps, who has seldom conquered nemesis Piersol in the backstroke. "No matter who I'm racing, I hate to lose."

The 23-year-old sports icon, in his first meet since winning a record eight gold medals at the Beijing Olympics last August, had not dropped a final since May 17 of last year when he lost to Piersol in the 200m back at Santa Clara.

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"He will definitely be motivated by this," said Bob Bowman, Phelps's coach. "He remembers the races more when he gets beat. It's nice for Michael to remember what it's like to race at the top level. That's good for him."

Phelps, who won 200 freestyle and 100 butterfly titles on Friday, completes his first meet on the way to the 2012 London Olympics with the 100 freestyle on Sunday. Phelps is ending a career-long nine-month layoff this week.

"I came back for all the races - win, lose or draw," Phelps said. "It was a good swim. Aaron and I are always going to have this back and forth. My legs weren't as strong as they should be. It's something to work on.

"For eight weeks of training, that's not bad."

Piersol was thrilled to continue his mastery over Phelps, who figures to swim the event more and more as he switches from endurance to speed events on his way to the next Olympics.

"I definitely wanted to win that," Piersol said. "With Mike, I figured he was going to do something big. He's always up for it. I have to have the same intensity. I'm confident in that race. I have a little more experience.

"It's one of the last frontiers for him. Mike is one of the only guys who has pushed me and shown me how much I can improve. Right now there is probably a little Japanese kid out there who is going to push both of us."

Phelps also qualified for the 50m freestyle final but withdrew after achieving his main goal of testing his new windmill-style sprint stroke.

The 23-year-old US star was second in his 50 free heat in 23.24 seconds. He kept his arms extended and flat to try and accelerate in an outside lane.

"It's more of a windmill than a standard bent-arm stroke," Phelps said. "It will help me get more tempo and turnover that I need."

World record-holder Fred Bousquet of France won the 50 free final in 21.33 seconds, matching the fifth-best all-time performance. American Cullen Jones was second in 21.92 with George Bovell of Trinidad and Tobago third in 22.01.

Bousquet said he considered Phelps as a potential sprint threat for years.

"I have seen him being a sprinter for a long time now," Bousquet said. "The guy can call himself a sprinter, that's for sure. I'm happy he decided to pay more attention to the 50 and 100."

Phelps was the last man in his 50-free heat to surface, something that helps in longer races but hurts in the splash and thrash event.

"I don't know how to swim a 50," Phelps said. "I saw the video. I can see a lot to change. My head position was too deep. I had a big wave over my head. It was a good first 50 of a 100. That's not a good 50.

"The underwater is not something you can do in a 50. I will work on it and see what happens."

After three weeks of high-altitude training in Colorado, Phelps will swim next month at Santa Clara and Montreal to prepare for July's US championships, the qualifier for July's world championships in Rome.