It was Necas’ first game since signing an eight-year contract with Colorado on Thursday.
Cale Makar had a goal and an assist, and Brock Nelson and Brent Burns also scored for the Avalanche (7-1-4), who have won two in a row after losing four straight. Scott Wedgewood made 22 saves.
Tomas Hertl and Mitch Marner each had a goal and an assist for the Golden Knights (6-2-3), who have lost three of four. Carl Lindblom made 22 saves in his second NHL game.
Necas gave the Avalanche a 1-0 lead 41 seconds into the first period with a one-timer off a Makar cross-ice pass.
Nelson extended it to 2-0 at 4:32 of the second period. Jack Drury took the puck off the bounce after a miscommunication between Ben Hutton and William Karlsson, then fed it to Nelson on the breakaway.
Hertl cut it to 2-1 during a 4-on-3 power play at 2:51 of the third period, sliding the puck underneath Wedgewood’s right pad after cutting across the crease.
Burns made it 3-1 at 10:11, finishing a wrist shot while trailing the play. It was the defenseman’s first goal since signing a one-year contract with Colorado on July 2.
Marner made it 3-2 at 12:01 after he sent the puck toward the goal from the right side before it bounced off Burns into the roof of the net.
Makar then scored an empty-net goal at 18:22 for the 4-2 final.
