Lehtonen was called upon to make 35 saves in the Thrasher's fifth win in their last seven games.
After nearly two periods of scoreless action, rookie defenseman Zach Bogosian got the game-winner with 2:28 remaining in the second and Todd White made it 2-0 before the period ended. Rich Peverley added an empty-net tally late in the third period.
Peter Budaj made 33 saves for the Avalanche, who now have lost seven of their last eight.
2014: The Year in Music [PHOTOS]