The Islanders lost the game and head coach Doug Weight, who was given a game misconduct after Landeskog's first goal.
Josh Bailey scored for New York, which has lost six straight on the road. Jaroslav Halak had 30 saves, including 19 in the second period when Colorado put a season-high 23 shots on goal. He was replaced by Thomas Greiss after two periods. Greiss stopped 12 shots.
The Avalanche took a 3-0 lead on goals by Nemeth, Nieto and Soderberg, and then blew it open at the end of the second period. Landeskog scored on the power play with 3:25 left, and after the goal Weight was venting to the officials when he was ejected.
That put Colorado back on the power play. After Scott Mayfield drew a crosschecking minor, Landeskog scored his second of the game and 16th of the season.
Bailey scored late in the third period to extend his points streak to 11 games.
Colorado RW Sven Andrighetto left in the third period with a leg injury. ... There was a moment of silence before the national Anthem for the Douglas County (Colo.) sheriff's deputies who were shot in an ambush Sunday morning, killing one and injuring four others. Douglas County deputies had been scheduled to present the colors for the anthem but were replaced. ... Avalanche C J.T. Compher is expected to miss at least a week with an upper-body injury suffered Friday night. ... Islanders C John Tavares had his nine-game points streak snapped. ... The Avalanche have killed off 33 straight penalties.