The 23-year-old from Kobe is the first woman since American Peggy Flemming in 1966, 1967 and 1968 to win three straight world golds, her triumph at the Centre Bell capping an unbeaten 2023-24 campaign.
Two 17-year-olds completed the podium, with American Isabeau Levito taking silver and South Korean Kim Chae-yeon grabbing bronze.
Sakamoto's charismatic routine packed with quality jumps had fans on their feet in Montreal.
He earned 149.67 points for the free skate for a total of 222.96.
That put her more than 10 points clear of Levito, who was second after the short programme and second in the free skate to finish with 212.16 points.
"I was fourth in the short program, so I was a little anxious about that, but today I was in a really good place emotionally," Sakamoto, who earned bronze at the 2022 Olympics before winning world gold in 2022 and 2023, told the crowd.
She said the key to her victory was maintaining her composure not only after catching an edge early in her programme but also as fans began to respond to her bold performance.
"I made sure I didn't get carried away and skated with composure," she said.
Kim, who was sixth after the short programme, took bronze with a total of 200.25 points as short programme leader Loena Hendrickx settled for fourth.
Levito said she was "in a state of shock" after completing her free skate.
"I had two goals coming into this world championship, getting on the podium and securing the third spot for the American women next year," she said.
"I did both. It was extremely satisfying," added Levito, whose result combined with teammate Amber Glenn's 10th-place finish ensure the US will have three skaters at next year's worlds in Boston.
Belgium's European champion Hendrickx, bidding to land gold after finishing with a sliver and a bronze at the last two, was eighth in the free skate to finish off the podium.
Earlier, Madison Chock and Evan Bates of the United States launched their ice dance title defense by topping the standings in the rhythm dance.
Chock and Bates, trying to complete their first undefeated campaign, received a season-best 90.08 points from judges.
The ice dance and men's deciding free skates will be contested on Saturday.
Two-time reigning European champions Charlene Guignard and Marco Fabbro of Italy, second at last year's worlds, were second in the rhythm dance with 87.52 points.
Canada's Piper Gilles and Paul Poirier, third in last year's worlds and winners in last month's Four Continents Championships at Shanghai, were third on 86.51 points.
The British two-time European runner-up duo of Lilah Fear and Lewis Gibson was fourth on 84.60.
Chock, 31, and Bates, 35, became a partnership in 2011 and are engaged to be married.
This year, they have won Grand Prix events on home ice and in Finland, taken the Grand Prix Final and also captured their fifth US crown.
