Pacioretty fired a forehand shot past Lightning goalie Mathieu Garon after P.K. Subban sprung him on a breakaway with a long pass, handing the Habs a 2-1 lead 7:17 into the middle frame.
Mike Blunden's goal less than 2 minutes earlier had forged a 1-1 tie for Montreal, which won consecutive games for the first time under Coach Randy Cunneyworth.
Erik Cole also found the net and Carey Price turned aside 23-of-24 shots in the win.
Tampa Bay's only goal went to Vincent Lecavalier and Garon finished with 25 saves as the Bolts dropped their third straight.
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