Rashard Lewis scored a game-high 28 points and Hedo Turkoglu shot 24 to help the Magic put away the NBA champions.
Paul Pierce led the Celtics with 27 points, after a paltry three-point return in game two.
Orlando, who squandered a 28-point lead in game one before closing out a 95-90 nail-biter, held firm as Boston made a late charge to cut a 20-point deficit to trail 83-75 with 10:15 left.
The Magic stepped up a gear, however, to put the result beyond doubt with an offensive run that left them leading 109-87 with three minutes on the clock.
Dwight Howard more than covered for the loss of suspended point guard Rafer Alston, shooting 17, and making 14 rebounds and five blocks for the Magic. Anthony Johnson chipped in with 13 points.
The teams head to Orlando for game four on Sunday.
