Pittsburgh fell behind 2-0 before rallying for their seventh straight victory. The Penguins have gone 19-4-1 over their last 24 games to climb within six points of the New York Rangers for the lead in the Atlantic Division.
Dupuis began the Pittsburgh rally by tipping in a shot from Matt Niskanen midway through the second period. Jordan Staal scored 1:34 into the third to tie it and Dupuis put a backhander past Jonas Gustavsson for the game-winner with 15:50 still to play.
Brad Thiessen, in only his second NHL appearance, made 22 saves and shut out the Maple Leafs over the game's final 32:14 to get the win. Thiessen also won his other start, which came against Columbus on Feb. 26.
Phil Kessel and Carl Gunnarsson scored for the Maple Leafs early in the second period, but they fell for the 12th time in 14 games.
Gustavsson allowed three goals on 33 shots.