ROME — Milorad Cavic can talk a good game. He's even better in the pool.

Cavic seized Michael Phelps' 100-meter butterfly world record today at the world swimming championships, where he's making plenty of headlines — in and out of the water.

First, the Serbian said he's tired of hearing complaints from the Phelps camp about competing in an inferior suit, even offering to buy him one of the polyurethane models responsible for most of the worlds records at the Foro Italico.

Then, Cavic went out in the semifinals of the 100-meter butterfly and knocked off Phelps' world record, nearly becoming the first swimmer to break 50 seconds. Phelps was the second-fastest qualifier at 50.48.

The two will be side-by-side tomorrow night in their rematch.

Cavic hasn't backed off on his belief that he beat Phelps to the wall at the Beijing Olympics, all photographic and timing evidence to the contrary. Now, the Serbian has another shot at the man who officially won by a hundredth of a second on the way to capturing eight gold medals in China.

"I didn't want to go out so fast, but I had so much energy in my body that I couldn't help it," said Cavic, who touched in 50.01 seconds to break Phelps' record of 50.22. "I'm capable of swimming under 50, which would be enough to win the gold."

Less than an hour after his 100 fly semi, Phelps claimed his third gold medal of the championships, swimming the leadoff leg of the 800 freestyle relay won by the United States with a world record of 6 minutes, 58.55 seconds — one-hundredth of a second faster than its gold medal time at the Olympics.

As for Cavic's offer to get him a faster suit, Phelps said he's content in his year-old Speedo LZR Racer.

"I'm wearing this," Phelps said. "If he wants to wear a different suit, he can throw this one on."

In the relay, Phelps was again no match for Germany's Paul Biedermann, who routed him in the 200 free and put his team more than 1½ seconds ahead on the first leg of the relay. But Phelps had the better supporting cast, teaming with Ricky Berens, David Walter and Ryan Lochte to set the sixth world record of the night and 35th of the championships.

Lochte, turning in an especially gutty swim after earlier taking bronze in the 200 backstroke, held off Russia's Alexander Sukhorukov with Phelps screaming at him from beside the starting block. When Lochte got there first, Phelps threw up both arms.

"I was kind of carried by my teammates tonight," Phelps said. "I was probably a half-second slower than I wanted to be. But these guys were able to take control. Lochte swam well the last 50. Ricky and David did a good job of putting us in a good spot."

Aaron Peirsol made up for a huge disappointment in the best way possible, obliterating the world record in the 200 backstroke and getting back at Lochte, who beat his fellow American in that event at both the 2007 worlds in Melbourne and last summer on the biggest stage of all.

This wasn't just any race for Peirsol, not after what happened Monday.

Expecting to cruise through to the final of the 100 back — after all, he was three-time defending champion and had just set a world record a few weeks ago — Peirsol made a huge miscalculation in how fast he needed to go. He finished ninth in the semis; only the top eight moved on the final.

Peirsol watched from stands the following night and started looking ahead to his other chance for an individual medal in Rome.

"It was kind of a blessing in disguise," he said. "I just didn't know it at the time"

Peirsol got out all his frustrations with a dominating performance, breaking his own world record by more than a full second, his time of 1:51.92 wiping out the mark of 1:53.08 he set at the U.S. nationals three weeks ago.

Japan's Ryosuke Irie claimed silver in 1:52.51, also under the old mark. Lochte faded to third.

"I wanted to race and I saw that I pulled out from the beginning and I was feeling all right," Peirsol said. "When I kept pulling away, there was even more of a fire to go a little faster."

Peirsol knew he'd done it before he even touched the wall. He spun around with a big smile and gave the water a roundhouse punch.

"Wooo!" the laid-back Californian said, showing a rare bit of emotion.

On the medal stand, Peirsol appeared to be struggling to hold back tears as the national anthem played.

Two Americans endured bitter disappointments.

Eric Shanteau, who put off treatment for testicular cancer after qualifying for Beijing, was edged out for gold in the 200 breaststroke by the narrowest of margins. He appeared to be ahead the final time his head popped out the water, but his glide to the wall was a little too long. Hungary's Daniel Gyurta touched in 2:07.64.

Shanteau's time was 2:06.65 — a hundredth of a second from his first world championship, and one that would have been especially poignant after what he went through last summer.

Rebecca Soni was cruising along in the women's 200 breaststroke, 1.5 seconds ahead of world-record pace halfway through a race she won in Beijing.

But Soni clearly went out too fast and left nothing in the tank for the finish. She shockingly fell from first to fourth on the last lap — out of the medals. Serbia's Nadja Higl raced by to claim gold, Canada's Annamay Pierse took silver and Austria's Mirna Jukic got bronze.

Four world records were set in the first three events of the night, not long after governing body FINA announced its ban on bodysuits would take effect the first day of 2010. It might take years, even decades to surpass the technology assisted times of these championships.

Germany's Britta Steffen broke her own record in the 100 freestyle at 52.07, having set the previous mark of 52.22 on the leadoff leg of the 400 free relay at these championships.

Britain's Fran Halsall claimed the silver, and Australia's Libby Trickett held on for bronze after going out strong. Americans Amanda Weir and Dana Vollmer were out of the medals in fourth and fifth.

After Peirsol's world record, the mark in the women's 50 butterfly dropped in consecutive semifinal heats.

Marleen Veldhuis of the Netherlands won the first semi in 25.28, eclipsing her own mark of 25.33 set in April. She got to keep the record less than 5 minutes — Sweden's Therese Alshammar won the next semi in 25.07.