Another swimming medal for Phelps, world record for Ledecky

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, posting a winning time of 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 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.

It was quite a night for the Americans, who were shut out on the golds on the opening night of swimming.

Racing nothing but the clock, Katie Ledecky gave the U.S. its first victory by crushing her own world record in the 400 freestyle.

The result was totally expected. The unassuming teenager from suburban Washington has dominated the longer freestyle events since winning gold in the 800 free at the London Olympics as a 15-year-old.

The only drama was whether she’d take the world record even lower.

Her powerful stroke quickly made that a moot point, too.

Ledecky kicked off the first wall with a lead of nearly a body length and steadily pulled away from the overmatched field — as well as the world-record line superimposed on the video screen.

Her arms churning effortlessly through the water, Ledecky touched nearly 5 seconds ahead of her closest pursuer and quickly whipped around to look at the scoreboard.

When Ledecky saw the time — 3:56.46 — she let out an uncharacteristic scream and shook her right fist. She crushed the mark of 3:58.37 that she set nearly two years ago on the Gold Coast of Australia, and had been chasing ever since.

“I was pumped,” Ledecky said. “That’s what I wanted and I had been so close to breaking that all year, the past two years. I knew I was due for a breakthrough.”

She’s just getting warmed up.

Ledecky, who added gold to the silver she won in the women’s 4×100 free relay, is also favored in other two individual events: the 200 and 800 free. In addition, she could pick up another gold in the 4×200 free relay.

It was a night of world records in Rio.

Britain’s Adam Peaty set his second mark in as many nights in the 100 breaststroke, while Sarah Sjostrom of Sweden eclipsed her own mark in the 100 butterfly.

Peaty won with a time of 57.13 that shattered the mark of 57.55 he set in the preliminaries. He cruised away from Cameron van der Burgh of South Africa, the defending Olympic champion who took silver this time in 58.69. The bronze went to Cody Miller of the United States, whose time of 58.87 held off teammate Kevin Cordes.

The crowd went into a frenzy at the sight of two Brazilians in the final. But Joao Gomes finished fifth and Felipe Franca was seventh.

Sjostrom led right from the start of the fly and touched in 55.48, knocking off the mark of 55.64 she established at last year’s world championships. She sat on the edge of the deck, pumping her arms in the air, and then appeared to be overcome by tears as she climbed to her feet.

This was her first Olympic medal. Sjostrom finished fourth in the 100 fly at the London Games four years ago, missing out on the bronze by just 23-hundredths of a second.

Penny Oleksiak of Canada took the silver in 56.46, edging out defending Olympic champion Dana Vollmer. The American, who had her first child 17 months ago, settled for the bronze in 56.63.

Already, six world records have been set in Rio.

The only mark that didn’t fall Sunday was the men’s 4×100 free relay.

Phelps and the Americans didn’t mind a bit.