BOSTON — Alysa Liu skated around the ice in disbelief, her golden dress shimmering in the lights of TD Garden, and the appreciative roar from a sellout crowd reminded her why she had returned to the sport following a nearly two-year retirement.

When her score was finally read, the 19-year-old from Clovis, California, had made history.

Liu became the first American women’s figure skating world champion in nearly two decades, dethroning three-time defending champ Kaori Sakamoto with a brilliant free skate Friday night. Her program to a rendition of “MacArthur Park” by Boston native Donna Summer earned her a standing ovation, and allowed Liu to finish with 222.97 points.

“I mean, it means so much to me and everything I’ve been through,” Liu said. “My last skating experience, my time away and this time around — I’m so happy, I guess. I’m mostly glad I could put out two of my best performances.”

Liu’s coaches, Phillip DiGuglielmo and Massimo Scali, pulled her into a hug in the kiss-and-cry area of the arena. Moments later, Sakamoto came over from where she had watched in the leader’s chair and squeezed her tightly, as if Japan’s hero was passing Liu the torch as the first world champion from the U.S. since Kimmie Meissner stood atop the podium in 2006.

“What the hell?” Liu asked in disbelief. “I don’t know. I don’t know how to process this.”

Sakamoto finished with 217.98 points to add a silver medal to her three previous golds. Her Japanese teammate, Mone Chiba, was third with 215.24 points while Isabeau Levito and Amber Glenn gave the Americans three of the top five.

“We are all so strong,” Levito said, “and we are all such fighters, and we all have our strengths, and are so different but we’re all so sweet with each other. I’m just so glad these are my fellow Team USA skaters.”

Liu was once considered the sport’s rising star, the youngest-ever U.S. champ when she triumphed at the age of 13 in 2019, and then defended her title the following year. She fulfilled a childhood ambition by qualifying for the Olympics, finishing sixth at the 2022 Beijing Games, and earned a bronze medal at the world championships that year.

Then she stepped away. Liu decided that skating had become less of joy and more of a job, and she wanted to focus on being a normal college student. It wasn’t until she went on a ski trip and felt the rush of competition — albeit in a much different way, and with far lower stakes — that she began to think about a comeback.

Early last year, she made it official with a cryptic posting on social media. And while the path back in a notoriously fickle sport was bumpy, to be sure, Liu took a big step forward with her second-place finish to Glenn at the U.S. championships.

She took the last step up on the podium Friday night.

“Not every yesterday, I didn’t expect this. I didn’t have expectations coming in,” Liu said. “I never have expectations coming into competitions anymore. It’s moreso, ‘What can I put out performance-wise?’ I really met my expectations on my part.”

She left Sakamoto, the erstwhile champion, with feelings of awe and admiration.

“She went away and now she’s back, and the world champion,” Sakamoto said. “I wouldn’t say she’s changed. Her cheerfulness and kindness and the way she’s always happy brought her to the stop step of the podium.”

Earlier in the night, American ice dancers Madison Chock and Evan Bates built a big cushion as they chase their third consecutive title, scoring a season-best 90.18 points for their rhythm dance to lead Canadian rivals Piper Gilles and Paul Poirier.

Gilles and Poirier scored 86.44 points to their dance, set to music from The Beach Boys. They held the lead only long enough for the U.S. duo to finish their “tour of the decades” program, which earned them a raucous ovation inside TD Garden.

The International Skating Union chose the theme this season of social dances and styles of the 1950’s, 60’s and 70’s. But while some skaters picked one — the Watusi, the Madison or disco — Chock and Bates threw it all into their rollicking showcase.

“It was probably the most fun I’ve had thus far on competitive ice in a performance, maybe ever,” Chock said. “It was really a joy to perform in front of a home crowd and share that excitement with Evan. It was the best.”

Now, Chock and Bates will try to finish off the first three-peat since Russia’s Oksana Grishuk and Evgeni Platov in the 1990s.

“That’s a tough amount of points to catch up on,” Poirier admitted, “but we also know that sport is really unpredictable.”