Jack Eichel had four assists, Mark Stone had a goal and two assists, and Shea Theadore had three assists for Vegas, which has won seven of its first eight season openers. Victor Olofsson scored twice in his debut after signing a one-year contract as a free agent on July 2, and Adin Hill made 27 saves.
Mikko Rantanen scored a hat trick, and Nathan MacKinnon and Samuel Girard each had two assists for Colorado. Alexandar Georgiev allowed five goals on 16 shots before he was replaced by Justus Annunen, who allowed two goals on five shots.
It was the season opener for each team.
Rantanen gave the Avalanche a 1-0 lead at 10:48 of the first period with a one-timer from above the left circle.
Olofsson tied it 1-1 just 27 seconds later when his wrist shot from a tight angle below the left circle beat Georgiev near side.
Barbashev put Vegas ahead 2-1 at 18:32 with a snap shot from the right circle.
Stone pushed it to 3-1 just 25 seconds later, finishing off a 2-on-1 rush with Eichel.
Rantanen cut it to 3-2 with a power-play goal at 4:15 of the second, beating Hill with a one-timer from the bottom of the right circle.
Zach Whitecloud made it 4-2 at 5:49 with a wrist shot from the top of the right circle.
Casey Middlestadt brought Colorado within 4-3 at 17:32, putting in a rebound with a backhand at the right post.
Olofsson made it 5-3 at 19:46 with a wrist shot from the right circle on the power play.
Rantanen completed his hat trick to cut it to 5-4 at 6:59 of the third period with a one-timer from the right circle on the power play.
Stone pushed it to 6-4 at 8:29 with a redirection in front off Eichel’s one-timer on the power play.
Barbashev extended the lead to 7-4 at 13:54 with a backhand off the rush.
Brett Howden scored an empty-net goal for the 8-4 final at 19:24.
