Tre Kronor's Olympic team captain, Landeskog, scored the 2-0 goal past compatriot Forsberg halfway through the first period.
Barely six minutes earlier, the NHL's leading scorer, Nathan MacKinnon, had scored his 41st goal of the season.
Forsberg, who kept a clean sheet against Calgary on Saturday, had so far allowed two goals on five shots. After that, the 33-year-old struggled for a long time, and Los Angeles was able to tie it 2-2.
But with less than five minutes left to play, the decisive goal came when Devon Toews made it 3-2 for Colorado. The final goal came into an empty net after Forsberg was picked off while searching for an equalizer.
