Phelps leaped past Larisa Latynina, an 18-medal winner in gymnastics for the former Soviet Union from 1956 and 1964. Latynina, 77, had planned to watch Phelps after attending the women's team final in gymnastics not far from Olympic Park.
Phelps had trouble describing his emotions afterward but he left no doubt how much he appreciated being able to share the moment with teammates. The swimmer huddled with the others afterward to thank them for being part of history.
"There's no better feeling than to do it with those guys," he said.
Phelps acknowledged feeling uptight at the start of the London Games and it showed when he finished a disappointing fourth in the 400 individual medley on the opening night of swimming.
The more he began to relax, the better Phelps has performed.
His teammates have taken notice. Phelps is "a little more like a human and not a machine this time," his coach Bob Bowman said.
Phelps swam a brilliant leg in the 400 relay Sunday when France's Yannick Agnel chased down Ryan Lochte to win in the final 25 meters.
With all the pre-Olympic hyperbole about the Phelps-Lochte rivalry, the Americans worked together to enjoy the momentous race Tuesday. Lochte gave the United States a strong lead just as Phelps had requested beforehand.
"We all wanted to get him a big lead so when Michael dove in he wouldn't have to work," Lochte said. "Anytime you can make history it's incredible."
Not that Phelps just cruised through the two laps without straining. He maintained the big margin to make sure his record medal became his 15th gold one.
The United States led from the start to finish in 6 minutes, 59.70 seconds. France finished second while China took third.
In Beijing, Phelps became the first swimmer to win eight gold medals and he has been a bona fide celebrity since. Now he has secured a place in sport that won't soon be forgotten.
For all the accolades, Bowman found the most satisfaction from how Phelps reacted to a bitter defeat in the 200 butterfly, an event he had won at two consecutive Olympics. Four years ago Phelps barely touched the wall ahead of Milorad Cavic in the 100 butterfly by finishing on a full stroke.
Tuesday night he miscalculated the final stroke as le Clos struck first to win in 1:52.96, well off Phelps' world record of 1:51.51. Phelps got the silver in a time of 1:53.01.
"Phelps is my hero and I love the guy," le Clos said. "To beat him, I can't believe it. You don't understand what this means to me. This is the greatest moment of my life."
It was not Phelps' favorite memory. But his teammates expected something special in the relay. "A mad Michael Phelps is a good one to have in the pool," teammate Ricky Berens of Charlotte, N.C., said.