Brandon Carlo and Torey Krug also scored for the Bruins, and backup goalie Anton Khudobin stopped 15 shots. Cassidy took over for fired coach Claude Julien on Feb. 7.
Kyle Palmieri and Devante Smith-Pelly had goals for the Devils, who dropped their sixth straight (0-4-2) as their playoff hopes continue to fade. Cory Schneider made 37 saves.
Spooner one-timed newcomer Drew Stafford’s pass from the right circle for the winner 8:18 into the period.