Australia and the US matched each other medal-for-medal on the first day of pool events at the World Championships.
The two meet favorites each won one gold, one silver and one bronze medal.
Ian Thorpe became the first gold medalist to emerge from the pool at the Palau St. Jordi.
The Australian "Thorpedo" comfortably demonstrated Sunday that he is still unbeatable in the 400m freestyle, finishing in 3 minutes, 42.58 seconds, more than a length ahead of silver medalist and countryman Grant Hackett (3:45.17). Dragos Coman of Romania took the bronze medal in 3:46.87.
Hannah Stockbauer of Germany won gold in the women's 400m freestyle (4:06.75). The US claimed top honors in the 400m freestyle relay (3:38.09) and Russia took the men's relay version.
On Monday, medals will be handed out in women's 100m butterfly, men's 50m butterfly, men's 100m breaststroke and women's 200m individual medley.
Thorpe's victory made him the first swimmer to win three straight world titles in the same event. His ninth gold medal also made him the first man to win that many in the worlds.
He immediately credited his new coach Tracey Menzies.
"Tracey told me just to concentrate on the ABCs and to make sure that I stayed in control for the whole race," Thorpe said. "I'm pleased with that swim. but it's the start of a long meet. I was very relaxed before the race."
Hackett was the last man six years ago to beat Thorpe at 400m in a major meet.
"I was disappointed thinking that my personal best could have actually got on top of Ian tonight," Hackett said. "It wasn't meant to be. It's a silver at the world championships and all in all it's not a bad start to the meet."
Stockbauer beat out silver medalist Eva Risztov of Hungary (4:07.24) and American Diana Munz (4:07.67).
Russia's team of Andrei Kapralov, Ivan Usov, Denis Pimankov and Alexander Popov won the men's relay in 3:14.06. The US took silver in 3:14.80, with bronze for France in 3:15.66.
Natalie Coughlin, Lindsay Benko, Rhiannon Jeffrey and Jenny Thompson made up the US' winning team in the women's relay. Coughlin's blistering opening leg set the pace for the victory and Thompson, the eight-time Olympic champion, closed out the race with a solid 100m of her own.
The Americans' winning time was 3:38.09. Germany won the silver in 3:38.73 with bronze for Australia in 3:38.83.
The diving wrapped up Sunday with two medal events.
Australia won gold in the men's 10m synchronized platform and China got it's fourth diving gold when it successfully defended the 3m women's springboard synchronized title.
Mathew Helm and Robert Newbery scored 384.60 points while Ukraine's Roman Volod'klov and Anton Zakharov took the silver with 372.60 points. Defending world champions and silver medalists from the 2000 Olympics, China's Tian Lian and Hu Jia, got the bronze with 367.14.
In 3m springboard synchronized, Guo Jingjing and Wu Minxia retained their world title.
The Chinese couple scored 357.30 points to beat Russian silver medalists Julia Pakhalina and Ilyina Vera (321.24).
Paola Espinosa and Laura Sanchez of Mexico took the bronze with 299.64 points.