Greg Stiemsma put in the game-winning bucket 75, in the preseason opener for both squads.
On the Raptors ensuing possession, DeMar DeRozan's 10-foot jump shot clanged off the iron and a put-back attempt by Andrea Bargnani was also off the mark, sealing the win for the Celtics.
Ray Allen paced the Celtics with 12 points, and Marquis Daniels netted 11 points. Kevin Garnett scored nine points and pulled down seven rebounds, while Jermaine O'Neil had eight points. Rajon Rondo dished out eight assists to go with five points.
Bargnani led the Raptors with 16 points and nine rebounds, while DeRozan dropped 14 points. Ed Davis contributed a double-double with 10 points and 10 boards, while Jerryd Bayless also chipped in with 10 points.