Brayden Schenn, Samuel Blais, and Vince Dunn scored for St. Louis.
Montreal goalie Carey Price made 26 saves. Jordan Binnington stopped 31 shots for the Blues.
The Canadiens, playing their third game in four nights, earned their first regulation victory of the season.
Tatar tipped a bouncing puck past Binnington in the first-period to open the scoring. It was his second goal of the season.
Schenn tied the game 1-1 with 2:03 left in the period, firing a shot that banked off the inside post past Price.
Less than a minute later, Drouin responded with a goal of his own. He skated into the offensive zone and fired a shot past Binnington as two Blues defenders closed in. Drouin has at least a point in each game he’s played this season.
The Blues tied the game in the second period when Blais scored a goal off a tight angle.
Dunn made it 3-2 by scoring a power-play goal 11 minutes later.
St. Louis’ advantage lasted less than three minutes. Danault tied it at 15:35 of the second period.
Lehkonen scored the eventual winner for Montreal at 7:30 of the third period. He wrapped around Binnington and jammed the puck underneath the goalie’s left pad, stabbing at it until it went in the net.
Gallagher and Domi added insurance goals in the third.
Blues: At Nassau Coliseum to face the New York Islanders on Monday.
Canadiens: Host the Tampa Bay Lightning on Tuesday.
Source: Fox Sports