After a scoreless first period, Pacioretty scored his sixth of the year at 1:53 of the second to put the Habs ahead 1-0.
Pacioretty intercepted a weak clearance by Pens defenceman Olli Maatta in the neutral zone, skated across the blue-line, and fired a low shot off the post and in.
Montreal opened the third period with two goals in quick succession.
Plekanec added to the Canadiens' lead at 1:05 when his wrist shot beat Fleury between the legs, and Pacioretty scored his second of the game a minute later after stealing a bouncing puck from Evgeni Malkin on the Pens' blue-line.
Pittsburgh reduced the deficit at 5:44 when Neal rifled a shot over Price's glove and into the roof of the net on the power play.
Neal added another late in the game, sidestepping Price and slotting his fourth of the year in the back of the net on the backhand at 17:07.
Montreal has now won three in a row and has outscored its opponents 12-6 during that stretch. The Habs are coming off a 3-2 victory against the Capitals on Friday in which they scored three times in less than five minutes in the first period to secure the victory.
The Canadiens travel to Buffalo to face the Sabres on Wednesday.
Notes: This was the first of three matchups between the Habs and Penguins this season. The teams meet again In Pittsburgh on Jan. 22. ... Sidney Crosby leads the league with 30 points. … P.K. Subban leads the Canadiens in points with three goals and 17 assists. … Habs defencemen have now gone seven games without scoring. … Pittsburgh sits first in the Metropolitan Division.