Six minutes and 54 seconds into the opening stanza, Finn Eeli Tolvanen got the visitors on the board.
The Canadiens then fell into some penalty trouble and were called for hooking twice in a row. Despite killing the first one, St-Louis' PK unit couldn't stop Daniel Sprong from making it 2-0.
Vince Dunn tripled his side's tally at 14:20 of the first period.
The Habs retreated to the locker room down 3-0. The shots were 19 to 6 in favor of the Kraken.
The second period featured no goals. The Kraken continued to dominate in shots with 35 against 15 after 40 minutes of play.
Still down by three, the Canadiens pulled Montembeault for an extra attacker near the end of the third frame, but Seattle netted a fourth goal to win 4-0.
The Canadiens netminder made 37 saves in the loss.
The Habs will honor former defenseman P.K. Subban on Thursday when they host the Nashville Predators on home ice.