ROME — He defiantly spit out a mouthful of a water, climbed atop the lane rope, pumped his fists furiously and tugged on that supposedly inferior swimsuit.

The message was clear: Don't mess with Michael Phelps.

Serbian Milorad Cavic tried to get in his head and wound up looking at his back, losing again to the guy who beat him at the Beijing Olympics.

This time, there was no doubt about it.

"There are always things that fire me up and motivate me," Phelps said yesterday, after becoming the first swimmer to break 50 seconds in the 100-meter butterfly. "That's just how I tick."

He stayed close over the outward lap and rallied on the return to beat Cavic with a stunning time of 49.82 at the world swimming championships. Cavic also broke 50 seconds, but 49.95 only got him a silver — and plenty of words to eat.

He wasn't nearly as close as last year's Beijing Olympics, when Phelps famously won by one-hundredth of a second on the way to eight gold medals, over Cavic's objections that he actually touched first.

"That satisfied me a little bit," Phelps quipped with that crooked grin of his. "I set it up perfectly."

His reaction was nearly as memorable. Phelps hopped on the rope that had separated him from Cavic — eyes searing, jaw jutting out. He pulled at both sides of his skintight LZR Racer swimsuit, letting his rival know that he heard about his offer to get Phelps one of those faster polyurethane suits so he wouldn't have any excuses if he lost in a Speedo.

No need, Milorad. Phelps did just fine with his own attire.

"I've never seen him that emotional," Phelps' coach Bob Bowman said.

The two rivals finally shook hands, but that was about it.

"He congratulated me and kind of smiled a bit, but I have a feeling that our battle is going to go back and forth for a while," Phelps said.

Cavic did say one thing to Phelps: "You're the man."

"He just looked at me and smiled," Cavic said. "He knows it."

Phelps has one event left — the 400 medley relay tonight, assuming the U.S. doesn't mess up in the morning prelims. The Americans will be a heavy favorite in that one, as always.

Three other world records were set yesterday, bringing the total to 39 with one day left at the final meet for high-tech bodysuits that have everything but a motor attached to them.

Kirsty Coventry of Zimbabwe took down her own mark in the 200 backstroke, winning in 2 minutes, 4.81 seconds. Russia's Anastasia Zueva also went under Coventry's old mark of 2:05.24, but 2:04.94 was only good enough for the silver. American Elizabeth Beisel claimed bronze.

China claimed the record in the women's 400-meter medley relay. Li Zhesi finished it off in 3:52.19 to beat the mark set by Australia (3:52.69) at the Beijing Olympics. The Aussies also went under the old mark, settling for silver in 3:52.58. Germany took the bronze.

The winning team also included Zhao Jing, Chen Huijia and Jiao Liuyang.

In a semifinal heat of a non-Olympic event, Britain's Liam Tancock set a world record of 24.08 in the 50 backstroke, eclipsing the mark of 24.33 held by American Randall Bal. Junya Koga of Japan also went under the previous record time to win the second heat at 24.29. The final is tonight.

After switching suits, going from Speedo to Jaked, 42-year-old American Dara Torres barely managed to qualify for the final of the 50 free. She was eighth fastest in the semifinals, claiming the final spot in today's race but not giving herself much chance to duplicate her silver-medal showing at Beijing, where she lost to Germany's Britta Steffen by one-hundredth of a second.

Meanwhile, the United States lost, 8-6, to Croatia in the bronze medal water polo match at the world swimming championships.

Paulo Obradovic broke a 5-all tie with 4:54 remaining in the game, and Igor Hinic's goal with 27 seconds left wrapped up the bronze.