Mark Schwarz explains why Michael Phelps' performance in the 4x100 freestyle relay should set the stage going forward at the Olympics for Phelps. (1:17)

RIO DE JANEIRO -- Michael Phelps has to clear out more space in his medal case.

Time to make room for gold No. 19.

With yet another dazzling performance, the most decorated athlete in Olympic history added to his staggering haul Sunday night in the 4x100-meter freestyle relay, giving the United States a lead it never relinquished.

"When I was on the block, I honestly thought my heart was going to explode out of my chest," Phelps said. "I was so hyped tonight and so excited."

With three individual events and likely two more relays left, Michael Phelps will surely take his medal count to heights that may never be matched. ODD ANDERSEN/AFP/Getty Images

Defending Olympic champion France was out front when Phelps dove into the water on the second leg, taking over for leadoff swimmer Caeleb Dressel. Even though the 100 free isn't one of Phelps' specialties -- he has never swum it individually at the Olympics, only in the relays -- he blazed down and back in a stunning 47.12 seconds, a time that was faster than all but the three anchors on the medal-winning teams, three of the best in the world at that distance.

"Coming off the wall I thought my kick-out was great," Phelps said. "I just wanted to hammer it, hit the touch and give them a bigger lead."

That he did.

Ryan Held kept the Americans in front before giving way to Nathan Adrian, the nation's best sprinter.

At that point, it wasn't really in doubt.

But Phelps wasn't taking any chances, pounding the starting block and shouting toward Adrian as the anchor made the turn for home.

When Adrian touched the wall first in 3 minutes, 9.92 seconds, Phelps thrust his right arm in the air and looked toward his infant son, Boomer, nuzzling in the arms of his mother, Nicole Johnson, the roaring crowd blocked out by the baby's noise-canceling headphones.

Little Boomer won't remember what his daddy did this night.

But that gold medal will never let him forget.

France took the silver in 3:10.53, while Australia claimed the bronze in 3:11.37, holding off a Russian team that was booed during the introductions -- a reminder of the drug scandal that has rocked the nation. Vladimir Morozov, initially banned from the Olympics, was one of Russia's relay swimmers.

Those ill feelings were pushed aside by the sight of Phelps once more climbing to the top step of the medal podium.

Phelps likely will take his medal count to heights that may never be matched by the time he's done in Rio.

He's still got three individual events, and will surely swim two more relays. Given the form he showed in his Rio debut, five more golds are certainly within reach. As it stands, he's got 23 medals overall.

"That's the fastest 100 free I've ever gone in my career, so I hope that's a good sign," Phelps said. "I guess we'll see over the next couple of days. But I'm very pleased with the start."

For Phelps, it was the fastest relay time he's ever produced at the Olympics. Faster even than 2008, when his Great Haul of China -- a record eight gold medals that broke Mark Spitz's longstanding record -- included a time of 47.51 in the 4x100 free relay.

At age 31, the guy can still amaze.

After the race, Phelps reached down to help Adrian out of the pool.

While he did it, millions of Americans watching at home saw several purple dots on Phelps' back and shoulder.

Some kind of new tattoo? Did he take a nap on a bed of tennis balls?

No, the circles are the result of cupping, a therapy technique that athletes use to help their muscles recover and perform at their best. It involves a therapist heating small glass cups, then placing them on the skin and pulling them from the body to loosen and relax the muscles.

Some experts are skeptical of the treatment's effectiveness, but Phelps has been using it regularly for a while.

Later, while taking that familiar victory lap around the pool -- a route he knows so well -- a single tear ran down his cheek.

Phelps no doubt was remembering the ups and downs of the past four years. A second drunken-driving arrest. Six weeks of therapy. Giving up alcohol. Getting engaged to Johnson. Reconnecting with his estranged father. Becoming a father himself for the first time.

Phelps retired four years ago, insisting he was done with swimming, only to return for what he calls his real farewell, the one that will send him out the way he really wants to go.

"It felt good to get my last 400 free relay of my career with this thing around my neck," he said. "It feels good to get it back."

Now, to make more room in the case.