But now he finally had another one of those necklaces. All was proper and correct in Phelps' world. He had won the 200-meter individual medley relay and defeating the man who smoked him last Saturday in another race, USA teammate Ryan Lochte.
Phelps edged out Lochte by 0.63 seconds in the rematch, the only other time they would face each other at these Games. For Phelps, this was also the third straight 200-IM victory at the Olympics. Nobody has ever done that.
"A pretty cool feeling, being able to three-peat," Phelps said. "You know, every one of these things is my last my last heat, my last IM, my last butterfly heat, my last semifinal. All my last."
That played into Phelps' relief, as well. He didn't want his last Olympics to be void of individual gold. Phelps will retire from all competition following these Games. He said so beforehand. He keeps saying so. It was nice of him to tell us, so we can savor watching one of the best athletes in American history.
After that first Phelps appearance last weekend, however, you wondered how much there would be to savor. In the 400 IM, the longer version of Thursday's race, Phelps faded to a shocking fourth-place finish. It raised memories of Willie Mays stumbling in the outfield with the New York Mets in his final seasons, or Brett Favre struggling on bad ankles in his last days with the Vikings.
Certain people including the person writing this column labeled Phelps' miserable defeat the end of an era. And it was. Phelps is plainly no longer the awesomely unbeatable swimmer he had been in 2008 or the supremely ascendant swimmer he had been in 2004.
Oh, Phelps is still among the best in the world. But not awesomely the best. Over the Games' first six days, Lochte has won more medals than Phelps. The only issue, after that lousy start, was how Phelps would perform the rest of the way, how he would conclude his career.
We received the answer Thursday. Phelps was not going to be embarrassed again. He stretched out his 6-foot-4 body and had his long arms out in front of everyone during the race's first yards of the first lap, the butterfly. He held the lead through the backstroke.
"I wanted to push the first 100 meters to see what would happen," Phelps said.
What happened was, swimming in the next lane, Lochte became excited and chased that pace, going out faster than he wanted to go instead of holding his energy for the last lap. Phelps stayed ahead in the breastroke and then plowed home in the freestyle to win.
Lochte touched the wall alongside Phelps, looked up at the clock and saw the inevitable. In their last race against each other, Lochte was second and Phelps was first. Lochte had stretched himself out with a bronze medal finish in the 200-yard breaststroke, which had to leave him a bit gassed. But Lochte refused to do anything except credit Phelps. The two men, who are the same age, have been respectful opponents.
"He's the toughest racer I've ever had to deal with," said Lochte. "It's going to be weird not swimming against him. He made history. And you know what? I'm happy to be part of that."
Phelps, to say the least, is not normally a reflective guy or deep thinker. But he was reflective late Thursday when asked to talk about the difficulty of becoming the first Olympian to earn 20 career medals, most of any human being.
"It's tough to get up and race against the best in the world in every single race," Phelps said. "It's cool to add this to my résumé tonight. It hurt."
Hurt him physically, Phelps meant. We don't think about often. We see how smoothly Phelps glides through the water on his freestyle stroke. We see how beastly and strong he is on the butterfly. We don't know what it must be like inside that skin when the muscles are screaming at him to stop and he instead overrides the internal screams to keep going.
Those screams will end this weekend.
"It will not be the same," said Laszlo Cseh, the Hungarian swimmer who won the bronze.
If you watched closely Thursday, you saw how Phelps is realizing the same thing. The medal ceremony after the 200 IM was 20th of his Olympic existence, his 16th gold medal ceremony. But he seemed to linger a little longer than at the previous 19 podium visits. Phelps stepped down and walked the length of the pool deck waving at friends in the crowd and at one point put up his index finger with the "No. 1" gesture, another rare sight.
Phelps has one more final individual race, Friday night in the 100-meter butterfly. He has one more relay race, Saturday night in the 4 x 100-meter individual medley relay. And that'll be it.
But at least, after Thursday's victory over the man who made him look so bad a few days earlier, we know the answer to the question. Phelps' career is going to end with an exclamation point. Not a period. An exclamation point. That is how it should end. That is what happens with champions.