Michael Phelps was unconcerned about posting only the second fastest time in morning heats for the 200-meter freestyle at the world championships Monday.

Paul Biedermann of Germany beat the swimmer who won a record eight gold medals at last year's Beijing Olympics.

Phelps won the final heat, but Biedermann's time in the previous heat was faster.

"That's fine. I'll be in the first heat tonight," Phelps said, looking ahead to the evening semifinals.

Three championship records were set in other events _ by Gemma Spofforth of Britain in the women's 100-meter backstroke, Rebecca Soni of the United States in the 100 breaststroke and Aschwin Wildeboer of Spain in the men's 100 back.

Six world records were set Sunday on the opening day of swimming at the Foro Italico, with this likely the last meet where bodysuits made of 100 percent polyurethane will be permitted.

Olympic silver medalist Matt Grevers barely qualified for the semifinals in the 100 back in 16th position after his TYR swimsuit split apart just before he jumped in the pool.

"I didn't completely freak out but definitely I was conscious of it," Grevers said, showing a two-inch rip by his lower back. "Luckily I made it in. Hopefully I'll do better tonight."

Biedermann won the 200 free heats in 1 minute, 45.30 seconds. Swimming his first individual event, Phelps clocked 1:45.60, and Danila Izotov of Russia qualified third in 1:45.86.

Phelps holds the world record of 1:42.96 set at last year's Beijing Olympics.

Olympic silver medalist Park Tae-hwan of South Korea qualified eighth, after missing the final of the event he won in Beijing _ the 400 free.

Biedermann broke Ian Thorpe's seven-year-old 400 free world record Sunday.

Phelps also won his first gold on the opening day in the pool, swimming the leadoff leg for the Americans in the 400 free relay.

"That felt really good coming off the relay. It felt really controlled for a morning swim," Phelps said. "We noticed yesterday that all the guys were swimming faster in the morning, so you have to kind of step up in the morning."

Biedermann doesn't have any designs on beating Phelps when it counts _ in Tuesday's final.

"I don't think it's going to be much of a duel at all," the German said. "He's a very good racer. I think he looked really relaxed this morning. From looking at the time he's in really great shape."

Still, Phelps was impressed with Biedermann's swim in the 400.

"I still can't believe the 400 free got broken. I thought that was the best record on the book," Phelps said. "It was crazy to see that go, but people are swimming fast. You usually don't see that in a post-Olympic year, but it's good for the sport. It makes it more exciting."

Wildeboer led the men's 100 back heats in 52.93, five hundredths faster than Aaron Piersol's previous championship mark.

Ryosuke Irie of Japan was second in 53 flat and Piersol, Liam Tancock of Britain and Japan's Junya Koga tied for third in 53.08

Piersol set the world record of 51.94 at the U.S. trials in Indianapolis earlier this month.

"I think a world record would win," Piersol said. "That would probably do it.

In the women's 100 back, Spofforth clocked 58.78, only one hundredth off Kirsty Coventry's world record set in last year's Olympic semifinals.

"I still can't quite believe that time," Spofforth said. "When I looked at the time I thought it was 59.78 and then I realized it said 58.78. I'm amazed, it just felt like a really smooth swim and I hope there's more in there for tonight."

Anastasia Zueva of Russia touched second in 59.01 and Coventry, the Olympic silver medalist from Zimbabwe, was third in 59.51.

American Natalie Coughlin, the Olympic and defending world champion, is taking this year off.

Olympic silver medalist Soni led the 100 breaststroke heats in a championship record 1:05.66. Leisel Jones held the previous mark of 1:05.72 set two years ago, and the Australian also holds the world record of 1:05.09, although she is sitting out these worlds.

Yuliya Efimova of Russia was second in 1:06.42 and Olympic bronze medalist Mirna Jukic of Austria was third in 1:06.58.

Lotte Friis of Denmark led the women's 1,500 free heats in 15:58.23.