MONTREAL (AP) – One week into the world championships, it’s finally time to go swimming.

And what a way to get things started Sunday: Michael Phelps vs. Grant Hackett, a showdown at 400 meters that has Phelps in the unusual role of underdog.

Phelps, who won six golds and eight medals overall at the Athens Olympics, wanted to take his remarkable repertoire in a new direction at these championships. So he set his sights on the 400 freestyle – one of the Australian star’s signature events.

“I’m looking forward to it,” Phelps said. “It’s going to be a fun race, exciting.”

With world record holder Ian Thorpe sitting out the worlds and Phelps a relative neophyte in the 400 free, Hackett is a clear favorite to win at this distance.

His entry time is nearly three seconds faster than anyone else in the field – and almost 41/2 seconds ahead of Phelps. But the 20-year-old American is eager to see how he stacks up against Hackett.

“Hackett has been very dominant in the middle distance freestyle events the past few years,” Phelps said. “It’s my job to step up and try to race him, go after it and see what happens. That’s one of the races I’m really looking forward to. Hopefully, we can get the ball rolling for the U.S.”

Three other swimming finals will be held Sunday night – the women’s 400 free, along with the 400 free relays for both men and women.

Eighteen-year-old Laure Manaudou of France is a huge favorite in the 400 free, looking to add to the gold medal she won in Athens last summer.

As for the relays, the Australian women look unbeatable. Jodie Henry, Alice Mills and Libby Lenton have three of the four fastest 100 times in history and should be able to hold off their biggest rivals, Natalie Coughlin and the Americans.

The U.S. men don’t face such daunting opposition in their relay.

The South Africans, who won gold in Athens with a world-record performance, decided not to enter the world championships because their team hasn’t been close to matching the form it showed last summer. Instead of an embarrassing letdown, they decided to let Ryk Neethling and Roland Schoeman compete for individual medals.

The Netherlands comes into the championships with the top entry time, just ahead of the Americans, but the Dutch don’t have their best swimmer. World record holder Pieter van den Hoogenband is skipping Montreal to recover from a hernia operation.

Phelps will lead the American team, which settled for bronze in Athens. The Aussies hope to bounce back from a dismal sixth-place showing at the Olympics, but they’ll have to do it without Thorpe swimming the anchor leg.

In lieu of another Phelps-Thorpe showdown, Hackett is stepping up to fill the void. The Aussie even added the 200 free to his already busy schedule, giving him a chance to go head-to-head with Phelps in two races.

“I’m used to racing the best,” Hackett said. “I’ve had to race Ian Thorpe over the last eight, nine years now, and we had many close battles. It’s a great challenge to be racing Michael. It’s something I look forward to.”

The Aussie has finished second in the 400 free at the last three world championships – each time losing to Thorpe. With his countryman out of the way, Hackett feels nothing can stop him from winning this year, not even the best swimmer in the world.

Phelps gave up two certain victories at these championships. He’s so far ahead of the world in the 400 individual medley and the 200 butterfly that he decided not to swim those, wanting to challenge himself by entering the 100 and 400 free instead. He’s still expected to swim eight events, the same number as Athens.

“It would be easy for him to take on the events he’s expected to win, but he’s after the competition,” said Dave Salo, the U.S. men’s coach. “He’s not afraid to lose.”

Phelps had hoped for another chance to race the “Thorpedo,” but the Aussie star has been on an extended break since Athens. Among his pursuits outside the pool: lobbying on behalf of New York’s unsuccessful bid for the 2012 Olympics.

Look for Thorpe to return for the 2007 championships, which will be held in Melbourne, as a lead-in to the Beijing Olympics the following year.

“He has sort of been who people know,” Phelps said. “A lot of my friends know who he is. Everybody is sort of disappointed he’s not here.”

But Phelps is here, eager to build on his already staggering accomplishments.

Two years ago, he rose to prominence at the world championships in Barcelona, winning seven medals and becoming the only swimmer to set five individual world records at one meet. Then came Athens, where he tied the record for most medals at a single Olympics and just missed Mark Spitz’s 1972 mark of seven golds.

“He’s abandoned his super-duper events,” said Bob Bowman, Phelps’ longtime coach. “I have put him at somewhat of a disadvantage, because he’s swimming some events in which he’s hardly favored.

“Of course,” Bowman added, “everybody will still expect him to win.”

AP-ES-07-23-05 1742EDT