Montreal won for the third time in four games, thanks in part to the first regular-season NHL goal by P.K. Subban. Carey Price made 34 saves for the Canadiens.
It was a 1-1 contest heading into the third, but Gionta scored while Zdeno Chara was in the penalty box for interference. Chara scored Boston's goal with 4:11 remaining in the first to forge the 1-1 tie.
Subban's goal came 5:19 into the contest on the power play. This was only the 18th regular-season game for Subban spread over two campaigns, but he did have a goal for Montreal during last year's playoffs.
Scott Gomez scored the final goal midway through the third period.
Tuukka Rask gave up three goals on 41 shots in what was Boston's third loss in four games.