Reigning NBA Most Valuable Player Gilgeous-Alexander scored 36 points in just under 34 minutes on the floor, sitting out overtime after missing nine games with an abdominal strain.
"Felt good," Gilgeous-Alexander said. "I'm just thankful to be back."
Jamal Murray scored 39 points and Nikola Jokic scored 23 points with 17 rebounds and 14 assists for the Nuggets, who led by as many as 16 in a tense, physical battle.
Thunder forward Luguentz Dort was ejected for a flagrant foul after he tripped Jokic, sparking a shoving match that saw Jokic and Oklahoma City's Jaylin Williams receive technical fouls.
Trailing 83-77 going into the fourth quarter, the Thunder had edged ahead 107-105 with 1:23 left in regulation before Jokic tied it with 38 seconds remaining.
Denver's Christian Braun came up with a big block on Gilgeous-Alexander and they went to overtime, Oklahoma City scoring the first five points in the extra session and hanging on for the win to maintain their two-game lead over the San Antonio Spurs atop the Western Conference.
"It was a great game," said Thunder center Chet Holmgren. "You want to play against the best players, the best teams, and they brought the intensity tonight."
Eastern Conference leaders Detroit also fought to a gritty overtime victory, topping the Cleveland Cavaliers 122-119.
The Cavs led by nine with less than three minutes left in regulation, but the Pistons clawed back and tied it on three free throws from Daniss Jenkins - who managed to fire up a half-court heave as Jaylon Tyson intentionally fouled him.
Detroit scored the first six points of overtime and held on for the win.
Jalen Duren led the Pistons with 33 points and 16 rebounds. Cade Cunningham added 25 points, 10 rebounds and seven assists before fouling out late.
Jarrett Allen led Cleveland with 25 points. Evan Mobley added 23 points and 12 rebounds for the Cavs, who were without recently acquired James Harden and top scorer Donovan Mitchell.
Harden missed a second straight game with a broken thumb and Mitchell was sidelined again with a groin strain.
The Pistons improved to 43-14 and hold a five-game lead over the Boston Celtics atop the East.
Celtics crush Nets
The Celtics bounced back from a sluggish loss to the Nuggets in Denver in emphatic style, connecting on 66.7 per cent of their shots from the field in a 148-111 home blowout over the Brooklyn Nets.
Jaylen Brown and Nikola Vucevic scored 28 points apiece and the Celtics drilled 22 three-pointers on 34 attempts.
The New York Knicks cruised to a 127-98 victory over the Bucks in Milwaukee to remain 1.5 games behind the Celtics in the race for second in the East.
Jalen Brunson scored 27 points and OG Anunoby added 24 for the Knicks, who had seven players score in double figures as they rebounded from a disappointing loss to the Cavs.
The Bucks had won eight of their prior 10 games to move within one game of the East's final play-in berth.
With Greek star Giannis Antetokounmpo still sidelined by a calf strain, Myles Turner led the Bucks with 19 points.
That included 18 in the first quarter, but the Knicks - fueled by Brunson's 22 in the first period - seized control and were up 77-57 at half-time, pushing the lead to as many as 32.
