Monday night he was seated in a waiting area, wearing a hoodie pulled over his scalp, scowling as a rival played head games in front of him.

Tuesday night he was standing atop the podium, sniffling as "The Star Spangled Banner" played, then laughing at voices in the crowd who sang it the Baltimore way.

Say this for Maryland's Michael Phelps, the fastest man in swimming: He can go from intense to joyous in the time it takes him to win a gold medal. And this one was special.

The most decorated Olympian of all-time outstretched Japan's Masato Sakai to capture a thrilling final in Phelps's signature event, the 200-meter butterfly, achieving an inconceivable milestone of 20 golds in his Olympic career. Phelps touched the wall first by four one-hundredths of a second—a blink of an eye and the narrowest margin of victory in the race's history, but still plenty of time to leave him wagging his index finger "number one" after seeing the results posted.

"This is a race I really wanted tonight," Phelps said. No doubt—the event is the first one he ever swam in the Olympics, and he finished second to South Africa's Chad le Clos in the 2012 London Games.

He had payback in mind. Le Clos shadowboxed next to Phelps before their semifinal Monday and couldn't take his eyes off of the American all week when they shared the same room.

Le Clos couldn't take his eyes off of Phelps during the final, either, looking up at one point to see his rival in front in the adjacent lane. The gold medalist bested him by seven tenths of a second. Le Clos finished off the podium, with Tamas Kenderesi of Hungary taking the bronze.

That victory was the difficult one for Phelps Tuesday night. He later brought the American team home as anchor in the 4x200-meter freestyle relay, holding on at the end for a comfortable two-and-a-half second win and a twenty-first gold medal.

He was back to work in the 200-meter individual medley Wednesday afternoon.