Reimer was busiest in the second period, when he turned aside all 16 Penguins shots to preserve a 1-1 tie.
The Leafs grabbed the lead early in the third when they intercepted an Evgeni Malkin pass and went on a 3-2 break. Kadri got a pass from Phil Kessel, faked Marc-Andre Fleury to the ice and put a backhander into the net.
Dave Bolland scored in the first period and added an empty-netter while Phil Kessel also scored for Toronto, which got back on the winning track following Friday's loss to Columbus.
Kris Letang scored and Fleury finished with 26 saves for Pittsburgh, which dropped a third straight.