Fowler, a 21-year-old rookie, was selected in the third round (No. 69) of the 2023 NHL Draft.
Cole Caufield scored for the third time in four games, and Lane Hutson and Juraj Slafkovsky each had two assists for the Canadiens (16-11-3), who lost 6-1 to the Tampa Bay Lightning on Tuesday.
Bryan Rust had a goal and an assist, and Tristan Jarry made 25 saves for the Penguins (14-8-7), who have lost three straight (0-1-2).
Alexandre Texier put Montreal ahead 1-0 on its second shot on goal at 2:54 of the first period, stealing the puck from Kris Letang and carrying it to the slot for a snap shot and his first goal this season.
Brendan Gallagher made it 2-0 at 4:37 of the second period by taking a cross-ice pass from Hutson in the left face-off circle for a wrist shot past Jarry’s blocker.
Caufield then extended the lead to 3-0 on a power play at 10:18 with a wrist shot from below the goal line that went in off Jarry’s skate for his 17th goal this season.
Owen Beck seemed to score his first NHL goal for Montreal at 16:21, but it was overturned when the play was ruled offside on a Pittsburgh challenge.
Rust cut it to 3-1 by chipping in a backhand pass from Sidney Crosby 44 seconds into the third period.
Oliver Kapanen scored 15 seconds later, tapping in Slafkovsky’s pass to make it 4-1 at 59 seconds.
Erik Karlsson pulled Pittsburgh to within 4-2 on a power play and with the extra attacker at 15:07, scoring his second this season on a point shot through traffic.