Olympic gold medalist Park Tae-hwan stuck with his old swimsuit and paid the consequences in the 400-meter freestyle.
The South Korean didn't qualify for the final after swimming in the opening session at the world championships on Sunday.
Park, who was also the defending world champion, touched in 3 minutes, 46.04 seconds _ more than three seconds behind leader Paul Biedermann of Germany, who then set a world record of 3:40.07 in the final.
Ian Thorpe's world record of 3:40.08 had stood for seven years.
Oussama Mellouli of Tunisia, the Olympic 1,500 free champion, finished second and Olympic silver medalist Zhang Lin of China was third.
Park signed a big contract with Speedo before the Olympics and he still wears the pant legs from last year's LZR suit. Many of the athletes in front of him opted for the new polyurethane suits from Jaked and Arena, considered the fastest now on the market.
"I wanted to start fast, but I just wasn't able to. I did my best but obviously I'm very disappointed," said Park, whose gold last year was South Korea's first ever in Olympic swimming.
Biedermann wore an Arena, and Park attempted to deflect the blame from his suit.
"I'm surprised, too. I couldn't get enough rest after the Olympics. I worked hard in 2005, 2006, 2007, 2008 with no rest," he said. "That was the problem."
Ryan Cochrane of Canada wore an Arena suit for the first time and qualified in seventh.
"It was a chance we took, but it worked out," said Cochrane, who won bronze in the 1,500 free at the Olympics. "It was a pretty fast heat and it's going to be an unbelievable final."
Ian Thorpe's world record of 3:40.08 has stood for seven years.
"There are five or six guys who can probably get close to that," Cochrane said. "I really believe that heats now are so much harder than they were five or six years ago. It takes a lot out of you to make the final, so it would be unbelievable if someone can do that today."
Park suggested he struggles in outdoor pools. The first day of swimming at the Foro Italico was held under a scorching sun, and Park also had trouble outdoors at the 2004 Athens Olympics and 2005 worlds in Montreal.
"It's some sort of a jinx I guess," he said.
In Athens, Park was disqualified for a false start in his 400 heat. At 14, he was the youngest member of South Korea's team in Athens and he was so upset he hid in a bathroom afterward for two hours.
Park didn't hide this time, stopping to speak with reporters for nearly 15 minutes.
"There was also a lot of pressure on me and I was nervous beforehand," he said. "But this could help me in the future."
Park is also planning to race the 200 and 1,500 free here.