Barbashev made it 2-1 at 11:22 when his wrist shot from the high slot beat Scott Wedgewood high to the glove side. Vegas forward Pavel Dorofeyev broke up Devon Toews’ clearing attempt up the boards, knocking the puck over to Jack Eichel, who passed to Barbashev for the finish.
Barbashev then scored his second of the game into an empty net at 18:57 for the 3-1 final.
Vegas leads the best-of-7 series 2-0. Game 3 is at T-Mobile Arena in Las Vegas on Sunday (8 p.m. ET; ESPN, SN, TVAS, CBC).
Barbashev also had an assist, Eichel had a goal and had an assist, and Dorofeyev had two assists for the Golden Knights, the No. 1 seed from the Pacific Division. Carter Hart made 29 saves.
Ross Colton scored for the Avalanche, the No. 1 seed from the Central Division and the Western Conference. Wedgewood made 22 saves.
The Avalanche were without defenseman Cale Makar, who missed his second straight game with an upper-body injury.
Colton gave Colorado a 1-0 lead at 16:59 of the first period with a wrist shot from the slot that went short side over Hart’s left shoulder. Colton skated around from behind the net and settled a bouncing puck after Kaedan Korczak blocked Brent Burns’ point shot.
Eichel tied it 1-1 at 9:15 of the third. Dorofeyev tipped Barbashev’s crossing pass to Eichel in the neutral zone, and Eichel took it straight to the right face-off dot before scoring with a wrist shot that went over Wedgewood’s right leg and in off the far post.
Vegas defenseman Brayden McNabb left the game at 13:40 of the first after a hit on Colorado defenseman Sam Malinski. He missed the entire second period but returned for the third and finished out the game.
