Novak won it with a one-timer after Egor Chinakhov chipped a loose puck to him in the slot.
Anthony Mantha scored twice in the third period, Chinakhov had a goal and an assist, and Erik Karlsson had three assists for the Penguins (32-17-14), who had lost three in a row (0-2-1), including 4-3 in a shootout to the Philadelphia Flyers on Saturday. Arturs Silovs made 22 saves.
Pittsburgh won for the fifth time in 19 games that have reached overtime.
Pavel Zacha had his second NHL hat trick, David Pastrnak ended an eight-game goal drought, and Viktor Arvidsson and Jonathan Aspirot each had two assists for the Bruins (35-22-6), who are 0-3-4 on the road since a 5-2 win at the Chicago Blackhawks on Jan. 17. Joonas Korpisalo made 34 saves.
Chinakhov cut it to 3-1 on a 5-on-3 power play at 14:44 of the second period with a wrist shot from high in the left circle.
Connor Dewar and Mantha scored 33 seconds apart early in the third period for Pittsburgh.
Dewar spun off Aspirot in the left circle for a backhand, cutting it to 3-2 at 6:02; Mantha scored on with a backhand on a semi-breakaway to tie it 3-3 at 6:35.
Zacha put the Bruins back in front 4-3 at 8:34 with a wrist shot off a pass from Arvidsson behind the net. He scored three goals in a 10-2 win against the New York Rangers on Jan. 10 for his previous hat trick.
Mantha tied it 4-4 at 11:18 by knocking down a point shot from Parker Wotherspoon and chipping it in from the crease.
Zacha put Boston ahead 1-0 on a power play at 9:27 of the first period, dropping to one knee in the right face-off circle for a one-timer.
Zacha made it 2-0 at 8:47 of the second period, stickhandling around Pittsburgh forward Ben Kindel before lifting a backhand over Silovs.
Pastrnak extended the lead to 3-0 at 12:23. Silovs retrieved the puck along the end boards and attempted a pass to Parker Wotherspoon that Pastrnak intercepted to wrap a backhand around the right post and off Silovs into the vacated net.