Olympic champion Park Tae-hwan of South Korea showed he's back in top form and Italy's Federica Pellegrini remained unbeatable in the 400-meter freestyle on the opening night of traditional swimming at the 14th FINA World Championships in Shanghai last night.

Michael Phelps' first race ended in disappointment, meanwhile, as the United States had to settle for bronze in the 4x100-meter relay behind surprise winner Australia and runner-up France.

Phelps' leadoff leg put the Americans second, but they dropped from there and Australia led from start to finish, with former sprint world record holder Eamon Sullivan holding off France's Fabien Gilot in the anchor leg.

It was the first time the American men failed to win a relay since the 2007 worlds in Melbourne, Australia, when Ian Crocker jumped in too early on an exchange in the morning heats, resulting in a disqualification.

The Netherlands won the women's relay with the same four swimmers who took the title at the 2008 Olympics and 2009 worlds: Inge Dekker, Ranomi Kromowidjojo, Marleen Veldhuis and Femke Heemskerk.

Park took the lead back midway through the men's 400 free then pulled away over the last two laps to touch in 3 minutes, 42.04 seconds, a distant 1.20 seconds in front of rising Chinese rival Sun Yang.

It was a sharp contrast from the last worlds in Rome two years ago, when Park failed to even make the final in this event. "I (was) glad to swim in lane one, which allowed me to fully concentrate on my own tempo and not to get distracted from the competition," the Korean said.

Defending champion and world record holder Paul Biedermann of Germany settled for third, 2.10 back.

In the women's race, Pellegrini was only fifth at the midpoint, but then surged into the lead one lap later and cruised to victory in 4:01.97.

Olympic champion Rebecca Adlington showed why she's a strong favorite for gold next year at her home London Games by taking silver, albeit a distant 2.04 behind, while Camille Muffat of France took the bronze, 2.09 back.

Cesar Cielo, the Brazilian cleared of doping by the Court of Arbitration for Sport three days ago, led the 50 free semifinals in 23.19.

Olympic champion Stephanie Rice of Australia led the 200 individual medley semifinals in 2:09.65. Ye Shiwen of China qualified third.