ROME: Olympic great Michael Phelps found all the motivation he needed to launch out on the long road to the 2012 Games at the swimming World Championships.

A defeat, and a dazzling victory over Milorad Cavic in the 100m butterfly will give Phelps plenty to focus on as he plots his next Olympic exploits.

He became the first man to break the 50-second barrier with a time of 49.82, reaffirming his superiority over the Serb after beating him by just one-hundredth of a second at the Beijing Games.

"The coolest thing is being able to have races like this, because it brings the best out of everyone," Phelps said of the tension-filled rematch.

"That's what sport is about, you have to go to the next level when racing these kind of people."

Phelps also won gold in the 200m butterfly, finally posting a world record that lived up to his lofty expectations in the event. Three relay golds took his total to five to balance his defeat by German Paul Biederman in the 200m freestyle.

"Michael's back in the game, which is good for us," said Phelps's personal coach, Bob Bowman, who was also head coach of the US men's team.

"I know for Michael you can expect anything, so I'm never really surprised," Bowman said. "He can always pull out something like the 100 fly when he really needs it."

In the wake of his glorious campaign in Beijing, where he earned a record eight gold medals to take his total to 14, Phelps took six months off.

He'd barely gotten back in the water when he found himself tabloid fodder - a London paper publishing a picture of him holding a marijuana pipe at a party.

A sprinkling of his sponsors tut-tutted, the USA Swimming federation slapped his wrist with a three-month ban, and the welter of negative publicity had Phelps saying he wasn't sure he wanted to swim on through the London Games.

Nor has all gone smoothly in the pool, as he tried, and finally rejected, a new freestyle stroke designed to help him become a player in the 100m free.

Phelps's personal uncertainties all played out against the backdrop of a costume controversy splitting the sport.

The debate over the super-fast polyurethane swimsuits gained a new intensity when Biedermann seized Phelps's 200m free world record while wearing one of the speedy models - which are headed to the scrapheap next year.

Biedermann ended Phelps's run of 10 straight individual victories in world and Olympic competition - a record stretching back to 2005 and including five individual golds at the 2007 World Championships and five in Beijing.

His last major defeat had been at the hands of compatriot Ian Crocker in the 100m butterfly final at the 2005 worlds.

"We're going to go back and work on the 200 free, that's a big motivator for him if he wants to race this kid," Bowman said.

And if Biedermann's victory inspired any doubts about Phelps's abilities, his scintillating victory over Cavic silenced them.

"When I was contemplating coming back, I remember watching some of the videos. I thought about the excitement I have when watching a race and after a race and the emotions that were going through my head.

"I wanted to get back to that, and this meet has brought me back to that. I think it's going to help me over the next few years," he said.

Bowman wasn't surprised to see his swimmer rise to the occasion against Cavic, who had needled Phelps over the swimsuit issue, snatched the American's recently achieved 100m fly world record in the semi-finals and told anyone who would listen that he still believed he had deserved gold in Beijing.

"He loves the big races, loves the energy," Bowman said. "He sort of thrives on that, while some other swimmers don't."

And Bowman was delighted to see what he'll have to work with as Phelps gets down to the serious build-up to London.

"It's very gratifying considering the year we've had and to know we're at that level starting the next season," Bowman said.

Cavic said the American remained the toughest man in the pool.

"Michael Phelps is Michael Phelps," Cavic said. "He does what he does - and he did."