Aaron Peirsol defeated fellow American Michael Phelps by 2.37 seconds with a world record in the 200m backstroke at the Pan Pacific Championships on Saturday night.
But Phelps wasn't down for long.
About 20 minutes later, he returned to lead off the US' 400 freestyle relay that set a world record.
In the backstroke showdown between the rivals, Peirsol touched in 1 minute, 54.44 seconds -- 0.22 seconds better than the mark he set at last year's world championships in Montreal.
"This is probably the best swim of my life," he said.
"Today was my day," Peirsol said. "I respect him [Phelps] for being in this race."
It's an event Peirsol has dominated since the 2000 Sydney Olympics, the last time he lost a 200. He won the 100 back on Thursday.
It was Phelps' first loss of the four-day meet, having won gold medals in the 200 butterfly, 400 individual medley and 800 free relay.
He was timed in 1:56.81. Tomomi Morita of Japan took the bronze.
"I knew I had enough energy to bring it home," Peirsol said. "I saw Michael next to me and I knew I had to start opening some distance. Without anyone next to me, I wouldn't have done that," he said.
The US led the medals standings after three days with 30, including a leading 16 gold. Japan was second with 17 and Australia third with 11.
Phelps had enough energy left over to team with Neil Walker, Cullen Jones and Jason Lezak for a world record in the 400 free relay. They won in 3:12.46 -- more than 3.5 seconds faster than Canada. Australia settled for bronze.
American Ian Crocker cruised to victory in the 100 butterfly. His time of 51.47 lowered the Pan Pac record he set in the preliminaries.
The US team of Amanda Weir, Natalie Coughlin, Kara Lynn Joyce and Lacey Nymeyer won the 400 free relay in 3:35.80, a Pan Pac record.
It was Coughlin's fourth medal and third gold.
The men's relay was the fourth world record of the meet, which ended yesterday. Phelps set a record in the 200 butterfly on Thursday, while Jess Schipper of Australia did the same in the women's race.
Schipper completed a sweep of the women's butterfly events, winning the 100 in a Pan Pac record time of 57.30 seconds. Americans Rachel Komisarz and Mary Descenza were second and third.
Ai Shibata of Japan defeated American Katie Hoff in the 400 freestyle. Shibata powered past Hoff in the final few meters and touched in 4:07.61.
It was Hoff's first defeat in three individual races, and her third individual medal. She anchored the US women to a gold in the 800 free relay on Friday.
Reiko Nakamura of Japan won the 200 backstroke in a Pan Pac record of 2:08.86.
Tae Hwan-park, a teenager from South Korea, won the men's 400 free in 3:45.72, overtaking American Klete Keller on the last lap.
Keller faded to third, earning a bronze to go with the gold he won in the 200 free.