ROME — Aaron Peirsol knew he’d gone fast enough before he even touched the wall. He spun around with a big smile and gave the water a roundhouse punch.

Not a bad way to get over a huge disappointment.

Peirsol smashed his own world record in the 200-meter backstroke Friday, looking every bit like a swimmer who was taking out his frustrations with every whirl of the arms.

“I had a lot of waiting around to do during this meet, and to swim so well in that final makes me feel really good,” Peirsol said.

He turned in an eye-catching performance even at a world championships where 35 records have fallen, breaking his own mark by more than a full second, his time of 1 minute, 51.92 seconds wiping out the mark of 1:53.08 he set at the U.S. nationals three weeks ago.

Japan’s Ryosuke Irie also went under the old record (1:52.51) but wasn’t even close to Peirsol.

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

Peirsol didn’t go fast enough on Monday — and shockingly missed the final of an event that he had won at the last three world championships and set a world record in less than a month ago.

Not realizing just how good the times would be, Peirsol was only ninth fastest in the semifinals, a stunning miscalculation that cost him a spot in the eight-man final.

Peirsol watched from the 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.”

The laid-back Californian let out a big “Wooo!” after touching the wall. On the medal stand, Peirsol appeared to be struggling to hold back tears as the national anthem played, a rare show of emotion for a guy who looks as though nothing ever bothers him.

“The world record time in incredible,” he said. “I have had that sort of time in my mind for a while, and have been waiting to do it for a long time.”

While Peirsol celebrated, teammates Eric Shanteau and Rebecca Soni had to cope with bitter disappointments.

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 of the water, but his glide to the wall was a little too long. Hungary’s Daniel Gyurta touched in 2:07.64.

“Of course I am disappointed not to get gold,” Shanteau said. “But I have a world championship medal and I have to be satisfied with that.”

Actually, he’s got two. Shanteau won bronze in the 200 individual medley, the first major medal of his career.

Shanteau’s time in the 200 breast 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.

“That was so hard,” he said. “I am exhausted. This has been a tough meet and I gave it all I had tonight.”

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 she clearly went out too fast and left nothing in the tank for the finish. On the last lap, Serbia’s Nadja Higl raced on by to claim gold, and two other swimmers passed Soni, too. She touched fourth — out of the medals.

“It was really painful,” Soni said. “I don’t really know what happened. Sometimes things don’t go as planned. This is a perfect example of that.”

Michael Phelps posted the second best time in the 100 butterfly semifinals, where he will go for gold tonight against Milorad Cavic, the same swimmer Phelps edged to win the event in the Beijing Olympics. Cavic broke the American’s world record in the semifinals.

Less than an hour after his 100 fly semi, Phelps took 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.

Phelps was again no match for Germany’s Paul Biedermann, who routed him in the 200 free and put his team more than 1 1/2 seconds ahead on the first leg. 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.”

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.