RIO DE JANEIRO — Australia turned to the best sister act in swimming to hold off an American team anchored by Katie Ledecky.

Give the gold to Cate and Bronte Campbell.

And a world record, too.

The Campbells carried their squad to victory in the 4 x 100-meter freestyle relay Saturday night at the Rio Olympics, with little sister Bronte snatching the lead from Dana Vollmer on the third leg and big sister Cate pulling away from Ledecky on the final down-and-back for a time of 3 minutes, 30.65 seconds.

The Aussies broke their own mark of 3:30.98 set two years ago.

That wasn’t the only world record to fall on a late night of swimming to kick off the Games. Shaking off repeated frustration on the sport’s biggest stage, Katinka Hosszu of Hungary crushed the world record in the women’s 400 individual medley to make the first Olympic medal of her career gold.

Also, Japan’s Kosuke Hagino ended American dominance in the men’s 400-meter individual medley, and Australia’s Mack Horton took down Sun Yang of China without giving his bitter rival so much as a passing glance.

The victories by Horton and the women’s relay team capped an impressive first night for an Australian team that captured only one swimming gold medal in London four years ago.

They've already eclipsed that total, with seven more nights to go.

Meanwhile, the powerful Americans managed three silvers but couldn’t reach the top step on the podium.

Simone Manuel and Abbey Weitzeil did their best in the relay, giving the United States a lead at the midway point. But Bronte Campbell was more than a second faster than Vollmer, who had competed about an hour earlier in the semifinals of the 100 butterfly, and Ledecky was no match for Cate Campbell, the world record-holder in the 100 free.

The United States had to settle for silver in an American-record time of 3:31.89, extending a gold medal drought in the event that goes back to the 1996 Atlanta Games.

Still, it gives Ledecky a strong shot at capturing five medals in Rio. She’s favored in the 200, 400 and 800 freestyle events, and could take another gold in the 4 x 200 free relay.

Canada claimed the bronze in 3:32.89.

Hosszu, known as the ‘‘Iron Lady’’ for her grueling schedule, had an especially sweet triumph. She had captured nine medals — including five golds — at the world championships but never won an Olympic medal. She defiantly pumped her chest before breaking into a huge smile.

She had led all the way and touched in 4:26.36, easily eclipsing the record of 4:28.43 held by China’s Ye Shiwen. Hosszu even had time to turn toward the scoreboard and watch Maya DiRado of the United States touch in 4:31.15 to take the silver medal. Mireia Belmonte Garcia of Spain claimed the bronze in 4:32.39.

Elizabeth Beisel of the United States, the silver medalist at the 2012 London Games, finished sixth.

Hagino took gold for Japan by holding off Chase Kalisz of the United States, becoming the first non-American to win the grueling event since 1992.

Hagino and Japanese teammate Daiya Seto raced away from the field on the butterfly and backstroke legs before Kalisz began to close the gap. The American surged past Seto on the breaststroke and set his sights on Hagino.

But the Japanese swimmer, who settled for bronze in this event at the 2012 London Games, held on to win in 4:06.05. Kalisz took the silver in 4:06.75, and Seto grabbed the bronze in 4:09.71.

Ryan Lochte was the defending Olympic champion, but he finished third at the US trials and didn’t even qualify. Michael Phelps was the champion in 2004 and 2008, but he’s dropped the 400 IM from his program. Tom Dolan was a back-to-back champion in 1996 and 2000.

Tamas Darnyi of Hungary won gold at the 1992 Barcelona Games.

Horton’s victory came at the expense of Sun, the defending Olympic champion. The Aussie grabbed the lead for good on the next-to-last lap and held off the hard-charging Chinese star, who won both the 400 and 1,500 free at the 2012 London Games.

What happened after the race was even more dramatic.

The bad blood between the two was on display for all to see as Horton celebrated after the race without even acknowledging the runner-up. Sun made a move as though he wanted to congratulate Horton, but the winner looked the other way.

They wound up climbing out of the pool side by side but never looked at each other. Horton’s winning time was 3:41.55, just 13-hundredths of a second ahead of Sun. Italy’s Gabriele Detti rallied past American Conor Dwyer, the top qualifier in the prelims, to take the bronze in 3:43.49.

After the prelims of the men’s 400 freestyle, Horton was asked about a reported incident between the two at the practice pool earlier in the week.

The Aussie said Sun ‘‘splashed me to say hello, and I didn’t respond because I don’t have time for drug cheats.’’

Sun served a three-month suspension for using a banned stimulant in 2014.

Horton and Sun finally gave each other a begrudging handshake on the medal stand.