Australian James Magnussen upset the men's 100m freestyle final with a thrilling victory over the Brazilian favorite Cesar Cielo Filho at the 14th FINA World Championships in Shanghai on Thursday.

The 20-year-old Magnussen, who ranked first in the semifinal, surpassed the others with strong stroke in the final spurt and touched home first with a minor advantage in 47.63 seconds.

The drug-cleared Cielo, both the world recorder and defending champion, failed to achieve a top three finish despite his lead in the first 50 meters.

The silver medal went to Brent Hayden of Canada at 47.95 and William Meynard of France finished third at 48.00.

"It's such an amazing thing for me. When I get back to Australia, I will meet my friends to relax myself. It sounds amazing to be called a world champion," said the winner.

"It has been six weeks before I could get a good night's sleep. No Australian has won this race in the world champs. It's good to be in the club with the two legends," he added.

The silver medalist Hayden, the fourth-placed finisher in the last Championships, said he was making progress step by step.

"I am faster than last year. It's good to win the medal. When I go home, I will train harder. Hopefully I will be better next year," the Canadian said.

Cielo, the first swimmer from Brazil to win an Olympic gold medal in Beijing, said he had tried his best.

"It is a strong final. But I tried as much as I could, I cannot think anything I can do to make it different.

"The London Olympics, it's still a long time. I need to first focus on tomorrow's game," the Brazilian said.

As one of the hot topics in the events, the Brazilian star swimmer was only cleared to compete in the championships last Thursday after a hearing by the Court of Arbitration for Sport following an appeal by governing body FINA to impose a doping sanction.

The Brazilian won the men's 50m butterfly on Monday.