William Karlsson and Jonathan Marchessault each had a goal and two assists, Shea Theodore finished with a goal and an assist, and Alex Tuch also scored a goal for Pacific Division-leading Vegas (48-21-7, 103 points).
The Golden Knights became the third expansion team since 1968-69 to make the Stanley Cup playoffs. The Hartford Whalers and Edmonton Oilers both accomplished the feat in 1979-80 after moving over from the World Hockey Association.
Fleury, who had 24 saves in the first two periods, improved to 28-11-4 this season. Vegas' Gerard Gallant earned his 200th career coaching victory.
Semyon Varlamov made 26 saves for Colorado, which won a 2-1 shootout over the Golden Knights on Saturday afternoon in Denver in the first half of the home-and-home set. On Monday, Erik Johnson scored his ninth goal of the season for the Avalanche (41-27-8, 90 points).
Tuch started the scoring at the 4:14 mark of the second period with a power-play goal. He swatted in a rebound of a Karlsson shot from the left side of the net for his 14th of the season.
Colorado tied it when Johnson buried a rebound of a Blake Comeau shot past Fleury's glove side at 13:41 of the middle period. Comeau nudged the Vegas goalie while skating through the front of the crease just before Johnson released his shot. The Golden Knights challenged for goalie interference, but the goal was allowed to stand.
On the ensuing faceoff, Colorado's Tyson Jost picked up a double minor for high-sticking when his stick got caught under the faceguard of Pierre-Edouard Bellemare and opened a nasty cut around the left eye of the Vegas winger. Marchessault scored his 25th goal of the season at 14:16 to give the Golden Knights a 2-1 lead.
Theodore scored his first goal in 32 games early in the third period to give Vegas a 3-1 lead, taking a pass from Erik Haula in the slot and firing a wrist shot over Varlamov's glove for his fifth goal of the season.
Karlsson sealed it with his 40th goal of the season, an empty-netter with 15.4 seconds remaining.
--Field Level Media
Colorado | Vegas | |
Erik Johnson 1 | Points | William Karlsson 3 |
Erik Johnson 1 | Goals | William Karlsson 1 |
Blake Comeau 1 | Assists | William Karlsson 2 |
N/A | Power Play Goals | Jonathan Marchessault 1 |
N/A | Short Handed Goals | N/A |
Semyon Varlamov .897 | Save Percentage | Marc-Andre Fleury .966 |
Semyon Varlamov 26 | Saves | Marc-Andre Fleury 28 |
Team | Shots | Goals | Power Play | Penalty Kill | Penalty Mins | Face Offs Won |
Colorado | 29 | 1 | 0-3 | 2-4 | 8 | 22 |
Vegas | 30 | 4 | 2-4 | 3-3 | 6 | 30 |