Phelps is 6-for-6 with two races remaining. His latest gold tied Australian Ian Thorpe's record from the 2001 worlds in Japan.

But Phelps failed to set a world record for the first time in five nights.

"I'm definitely starting to feel it (fatigue)," he said. "I've got to get some food and some sleep, and hopefully tomorrow I'll run off adrenaline. I need to come back and do two solid races."

Still, it was another dominating night for the United States.

The Americans won four of the six finals, including 1-2 finishes in the men's 100 fly and men's 50 freestyle. They have a leading 31 medals, including 17 gold with one night remaining. Australia is second with 17 medals and seven golds.

As the two-time defending champion and world record holder, Crocker was the one guy who could've stopped Phelps' gold rush. But it didn't happen.

Crocker was first at the turn, with Phelps third — the first time in four individual races that he didn't zoom to the lead. But he sure came home hard.

"Ian has more speed than I do. I know that he goes out hard and I wanted to close that gap," Phelps said.

He caught Crocker in the final furious strokes — touching in 50.77 seconds and joining his rival as the only men to break the 51-second barrier. Crocker hit the wall in 50.82. Albert Subirats of Venezuela took the bronze.

"It's never quite the race you want," Crocker said.

Phelps had never beaten Crocker at worlds — taking silver behind him in 2003 and 2005. In between, Phelps denied Olympic gold to Crocker in Athens by four-hundredths of a second.

"That's how I won the Olympic medal," Phelps said. "You have to nail the finish as best you can. I actually thought I botched the finish, but it ended up being good enough."

Crocker swam over to Phelps in lane six and shook his hand. On the podium later, Crocker looked a bit glum while accepting the silver medal.

Phelps had a grin plastered on his face during yet another victory stroll as Christina Aguilera's "Ain't No Other Man" blared. He whipped a stuffed penguin into the stands and a young woman excitedly scooped it up.

American teenager Kate Ziegler overtook Laure Manaudou of France on the final lap to defend her title in the 800 freestyle.

Manaudou was under American Janet Evans' 17-year-old world record through 400 meters before falling off the pace, with Ziegler nearly matching her stroke-for-stroke.

The women were dead-even after 550 meters and traded the lead twice more before Ziegler came home first in 8 minutes, 18.52 seconds — the second-fastest time ever. Manaudou, the 200 and 400 free champion here, took the silver in 8:18.80.

American Hayley Peirsol earned the bronze.

Australia's women beat the United States in the 400 medley relay and lowered their world record, too.

Emily Seebohm, Leisel Jones, Jess Schipper and Libby Lenton touched in 3:55.74, bettering the old mark of 3:56.30 at the Commonwealth Games in Melbourne last March.

Americans Natalie Coughlin, Tara Kirk, Rachel Komisarz and Lacey Nymeyer took the silver in 3:58.31 — the country's fourth consecutive runner-up finish.

China earned the bronze in 4:01.97.

Coughlin had the Americans in front and 0.40 seconds under world-record pace on her opening leg of backstroke.

But Jones, the 100 breaststroke world champion, outraced Kirk and put the Aussies in front for good. Lenton, the 100 freestyle champion, cruised home with Nymeyer in her wake.

American Ben Wildman-Tobriner conquered swimming's most chaotic 22 seconds, winning the 50 free in an upset over more heralded teammate Cullen Jones and defending champion Roland Schoeman of South Africa.

Wildman-Tobriner touched in 21.88 seconds; Jones at 21.94 for the silver.

Stefan Nystrand of Sweden earned the bronze. Schoeman faded to seventh.

"It's hard not to be disappointed when you're kind of the favorite going in and you get second," Jones said. "It does leave a sour taste in your mouth, but coming in second to your own teammate definitely softens the blow a little bit."

Wildman-Tobriner was only sixth-fastest coming into the final, while Jones was second-fastest.

"There was zero pressure on me," Wildman-Tobriner said. "Honestly, it's not a surprise to me. Hitting the start well, which I have been struggling to do, I knew I would definitely have a good chance. When I hit the water, I felt it was right. It gets you fired up for rest of the lap."

Jones gained major attention by winning the 50 free at the Pan Pacific championships in August (Wildman-Tobriner was fifth), and the black swimmer wanted a world title to further his goal of getting kids of all colors interested in the sport.

"Anything I do, as long as I'm trying to promote diversity in swimming, I think is going to help no matter what," Jones said. "I just hope this is not a trend. At world short course, I got silver. Here I got silver. Hopefully, at the Olympics I get gold."

Wildman-Tobriner goes by a combination of his mother's maiden name and his father's name. The 22-year-old Stanford swimmer's first international gold medal came at the 2005 worlds, when he swam on the 400 freestyle relay in the morning. He also swam preliminaries of the 400 free here, earning a gold.

Margaret Hoelzer of the United States ended her runner-up streak in the women's 200 backstroke, winning with the second-fastest time ever — 2 minutes, 7.16 seconds.

The former Auburn swimmer who turned 24 Friday had finished second at the 2003 and '05 worlds, where she was beaten by Kirsty Coventry of Zimbabwe.

"It is exciting to finally kind of get past that second place, finally move up and see what it feels like," she said. "To see everybody else swim well makes you want to swim well and try to sort of live up to what everybody else is doing."

Coventry led the first 100 meters before Hoelzer edged ahead at the third turn. Coventry settled for silver in 2:07.54. Reiko Nakamura of Japan was third.

Therese Alshammar of Sweden won the women's 50 butterfly — a non-Olympic event — in 25.91 seconds for her first world title at age 29.

Danni Miatke of Australia took the silver. Inge Dekker of the Netherlands earned the bronze. Komisarz was fifth.

Thorpe was in the stands, surrounded by the Australian team, hours after the shocking news broke that he had a suspicious doping test just months before retiring last year.