For the second consecutive night, he won an event for the third Olympics in a row.
He didn't match his record eight gold medals from Beijing four years ago. But Phelps has won three gold and two silver medals in six races in London after taking time away from the pool. When he looks back, the Baltimore swimmer might someday appreciate what he accomplished here even more than in 2008.
"I said I wanted to change the sport and take it to another level," Phelps said.
Almost everyone agreed that he reached that goal hands down.
The most decorated Olympian in history was well off his world record of 49.82 seconds in the 100 butterfly. But Phelps' time of 51.21 seconds was ahead of South Africa's Chad le Clos and Russia's Evgeny Korotyshkin, who tied for the silver medal. Cal graduate Milorad Cavic of Serbia tied for fourth four years after pushing Phelps to the brink in the same race.
But as Phelps' career is on its final leg, swimmers thought only of what he has meant to them and the sporting world.
"Michael has done more for this sport than any swimmer or group of swimmers have done," Cavic said. "I can't even put myself in the equation because he's on a different level than I am."
Phelps turned London into a farewell tour where for the first time he hasn't been afraid to express his feelings. He got choked up on the victory podium Friday but expects to become even more emotional Saturday when it comes to a dramatic ending.
For three Olympics, Phelps has worn a business-like demeanor. For the past week and a half, he has smiled, joked and enjoyed the moments, even turning his camera phone on hundreds of reporters. "You're always taking pictures of me; I want some of you," he quipped.
It was easy to understand Phelps' impact on his fellow athletes.
South Africa's le Clos became emotional when describing how three years ago he labored to make his country's national team just so he could swim against his childhood idol.
"It's crazy to think that he's retiring because I've always looked up to him. It's going to be hard to go to a meet now and think that he's not there."
Phelps plans to be there, though. Just not in the pool. He can't wait to watch from the sideline to monitor how the sport progresses.
"I'm leaving at a good time," said Phelps, who predicted new Americans will continue on the trail he blazed.
He's more optimistic than most because it is difficult to imagine another Olympian with such breadth of talent coming along any time soon.
"He's pushed all of us," said Cullen Jones, who won the silver medal in the 50-meter freestyle Friday. "He's put up times all of us strive to achieve."
Florent Manaudou won the sprint in 21.34 seconds, with Jones trailing in 21.54 seconds. Brazilian star Cesar Cielo touched .02 of a second behind Jones for the bronze medal.
Anthony Ervin of Berkeley, the 2000 champion, took fifth after taking 12 years off between Olympic competitions.
"Just being here at all is a dream come true," he said. "By being here, it is my own form of redemption."
Phelps' redemption came after finishing fourth on opening day in the 400 individual medley. Since then, he has been superb every time he leapt off the starting block.
His shadow is so large it clouded out perhaps the London Games' most surprising swim result. Katie Ledecky, another Maryland swimmer, won the women's 800 freestyle Friday by routing world-record holder Rebbeca Adlington of Great Britain.
Ledecky, 15, won in 8:14.63, half a second off the world mark. Spain's Mireia Garcia Belmonte won the silver, while Adlington got the bronze. Cal graduate Lauren Boyle took fourth for New Zealand, 9.23 seconds behind the winner.
Ledecky recalled meeting Phelps when she was 6. Then she credited him with calming her down just before the race.
She never could have imagined stepping to the victory podium on the same night as Phelps, who can't wait to put aside the singular diet of pasta and pizza for life's variety.
He promised to stay in shape, though. The slender 6-foot-4 swimmer also promised to remain visible.
But it's not as if he could simply disappear like a sunset.
History's most relevant swimmer isn't an afterthought just yet.