BUDAPEST, Hungary >> Katie Ledecky is off to a golden start at the world championships.

Make it a double.

The 20-year-old American star began an audacious week by winning a pair of gold medals today on the opening night of swimming along the Danube River. She cruised to a dominating victory in the 400-meter freestyle and put the U.S. ahead to stay in the 4×100 free relay.

Anchored by Nathan Adrian, the American men also won gold in the 4×100 free.

“It was a good first night for Team USA,” Ledecky said. “I’m happy with my two swims and how it all went.”

The only blip of a disappointment: Ledecky didn’t break the 400 free world record she set last summer at Rio de Janeiro. That merely demonstrates what a high standard she’s set.

For the most part, her only competitor is the clock.

“It’s my second-best time,” Ledecky said. “There’s no disappointment. It’s a world championship gold medal and there’s nothing to complain about there.”

Ledecky touched in 3 minutes, 58.34 seconds — more than 3 seconds ahead of U.S. teammate Leah Smith but nearly 2 seconds off the world record (3:56.46) from the Olympics. China’s Li Bingjie claimed the bronze.

About an hour later, Ledecky returned to the pool for the relay, a down-and-back sprint that is the weakest of her distances, but one that provides an opportunity to equal Missy Franklin’s female record of six gold medals at the 2013 worlds.

Ledecky turned in the slowest split on the American team, actually slipping to third on her 50 flip. But she powered back to the front by the time she passed off to Olympic champion Simone Manuel, who closed it out for the Americans.

Sarah Sjostrom set a blistering opening pace for Sweden, taking down the first swimming world record of the championships with a split of 51.71. She eclipsed the 100 free mark of 52.06 set last year by Australia’s Cate Campbell.

But Sweden didn’t have enough speed on the back end and faded to fifth. Manuel touched in 3:31.72, anchoring a team that also included rising star Mallory Comerford and Kelsi Worrell.

The U.S. took three of the first four swimming events, holding off hard-charging Brazil in the men’s relay. Caeleb Dressel went out more than a second faster than anyone on the opening leg, and Adrian brought it home with Bruno Fratus right on his left shoulder.

At the worlds two years ago, the Americans stunningly failed to qualify for the final in Kazan, a huge embarrassment for the swimming superpower.

Now, they’re back on top of the world.

“There’s a legacy that was left for us to take over,” said the 28-year-old Adrian, the senior member of a squad that also included Townley Haas and Blake Pieroni. “I know when I leave, it will be in good hands.”

The winning time was 3:10.06 — just 0.28 ahead of the Brazilians. The crowd saved its biggest cheers for the bronze medalist, rocking Duna Arena when Hungary rallied for a spot on the podium.

In the first final of the night, China’s Sun Yang got a bit of payback for his Olympic defeat in the men’s 400 free, pulling away from rival Mack Horton of Australia.

Yang was in a league of his own in a stacked field that featured the past three Olympic champions: Horton (2016), Sun (2012) and South Korea’s Park Tae-hwan (2008).

“I have no exact target for the week,” the 25-year-old Sun said through an interpreter. “I’m in a lot of pain. I’ve been training a lot for the last year. I’m also getting old, so there are a couple of injuries here and there. I’m always wrapped up in tape after every competition.”

The Chinese star finished more than two body lengths ahead of the field, finishing in 3:41.38. Horton settled for the silver, far back at 3:43.85, while Park finished fourth behind bronze medalist Gabriele Detti of Italy.

Horton defeated Sun in the 400 free at Rio after calling him a “drug cheat” over his three-month doping suspension in 2014. The Aussie has made it clear he doesn’t think anyone who tests positive should be allowed to compete — which also applies to Park, who served a doping suspension that ended before the 2016 Olympics.

“I’m just going to focus on what’s happening this week and do my best,” Sun said.

Horton shrugged off his loss to Sun, saying “the most disappointing thing for me was the time.”

“Placings didn’t really matter this year,” the runner-up said. “I just would have liked a faster time, but I guess it means I have stuff I can work on over the next couple of years.”