-- The United States out-touched Australia to win the men's 800-meter freestyle relay after Michael Phelps withdrew from the World Short Course Championships because of a back injury Friday night.

Justin Mortimer overtook Australia's Joshua Krough in the final 25 meters and got his hand on the wall first. Ryan Lochte, Chad Carvin, Dan Ketchum and Mortimer were timed in 7 minutes 3.71 seconds. Nicholas Sprenger, Andrew Mewing, Brendan Hughes and Krogh finished in 7:03.78. Brazil was third.

Phelps, an eight-time Olympic medalist, had planned to swim the relay after pulling out of the 400 individual medley preliminaries Friday morning. He won the 200 freestyle on Thursday, opening night, and in the process aggravated a sore back that had bothered him for 11/2 weeks.

"I don't think this is a big issue," Phelps said. "I just want to be extra cautious and extra safe."

Sprenger gave Australia an early lead before Carvin put the Americans in first. With 50 meters remaining, Krogh had the Aussies back in front by two-tenths of a second before Mortimer surged past him in front of 8,782 cheering fans at Conseco Fieldhouse.

The Americans won five of eight finals Friday, giving them 10 wins in 13 events. They were 5 for 5 Thursday. However, the United States' medal count is likely to be lower because of Phelps's withdrawal. He was set to swim in five individual events and some relays.

"Thank goodness it was here and not at the Olympics," Aaron Peirsol said.

Peirsol, who swept the backstroke events at the Athens Olympics, won the 100 back.

He was on world-record pace coming off the final turn in the 25-meter temporary pool and finished in 50.72, lowering the meet record of 50.75 set by American Neil Walker in 2000.

"I didn't expect anything less," Peirsol said. "It feels good to come out on top."

Australian Matt Welsh, who was fifth in the 100 back in Athens, finished second and Thomas Rupprath of Germany was third.

Without Phelps in the 400 IM final, Oussama Mellouli of Tunisia won in 4:07.02. Eric Shanteau of Lilburn, Ga., was third.

"Without Michael in there, it makes it less of an intimidating field," Shanteau said.

It was the first gold medal in an international swimming meet for the Mediterranean country. Last year, Mellouli earned a bronze in the world championships.

"That just makes it unbelievable," said Mellouli, who swims for Southern California. "There was so much pressure on me coming in. I was seeded first, but after the prelims I was only sixth. Deep down, I knew I could win it."

Olympic silver medalist Ian Crocker won the 100 butterfly in a meet record 50.18. James Hickman of Britain was second in 51.13. Benjamin Michaelson of Seymour, Conn., was last in the eight-man field.

Olympic gold medalist Natalie Coughlin withdrew before the meet after injuring her foot in training.

Haley Cope of Chico, Calif., who was eighth in the 100 back at Athens, won the event in 59.03, ahead of China's Gao Chang. Olympian Margaret Hoelzer of Huntsville, Ala., was fourth.

Brendan Hansen made up for his Olympic disappointment with a victory in the 100 breaststroke. He finished in 58.45, ahead of Australian Brenton Rickard in 58.64. Hansen broke the world record in both the 100 and 200 breaststroke at the Olympic trials, but finished second in the 100 and third in the 200 at Athens.

Sachiko Yamada of Japan won gold in the 800 free, finishing n 8:18.21. Kate Ziegler of Great Falls led early and touched second in 8:20.55.

Michael Phelps, en route to victory in the 200 freestyle Thursday night in the World Short Course Championships: "I just want to be extra cautious and extra safe."