Plekanec deflected a shot by the 6-foot-6 son of former NHL defenceman Mark Tinordi past Johan Hedberg at 6:49 after the goalie made an ill-advised clearing attempt from behind his net. Tinordi got the puck above the left circle and let it fly.
Colby Armstrong also scored for Montreal, and Carey Price made 32 saves. The Canadiens moved into a tie with Pittsburgh for the most points in the Eastern Conference.
Defenceman Peter Harrold scored for New Jersey, which lost for the second time in two nights (0-1-1).