Hedo Turkoglu(notes) nailed four of the 13 three pointers as the Magic had a 16-4 run in the first quarter then pulled away for good in the fourth.
Turkoglu finished with 25 points and 12 assists while Dwight Howard(notes) had 12 points and 16 rebounds.
"We got a good victory," Howard said. "It feels good."
The Magic now take their balanced attack to Cleveland where they will face LeBron James´(notes) Cavaliers in game one of their best-of-seven, semi-final series on Wednesday. The winner goes to the NBA finals.
"It is going to get harder but we believe we can go all the way," Howard said.
Turkoglu had the magic hand Sunday, scoring 10 of his 25 points in the fourth and going nine for 12 from the field.
Orlando seized a 14-point lead in the second quarter before Boston cut it to 45-42 in the third.
"I would like to say we played the game exactly the way we wanted. We actually played it better," Magic coach Stan Van Gundy said. "When you look at a team that´s 32-0 when leading a series 3-2 and then you win by 19 points, that´s a big win.
"I can´t say that I´ve ever had one that I´ve ever been happier with."
The Celtics were playing without injured star Kevin Garnett(notes) who sat out the series with a right knee strain. Now that the series is over Garnett is expected to have surgery.
Ray Allen(notes) led the Celtics with 23 points while Paul Pierce(notes) added 16.
"We still felt like this was a team that could have gone to the championship and won it, regardless of the injuries," Pierce said. "It felt like we ran out of gas."
Howard took a seat on the bench with just over eight minutes remaining and the Magic up 81-64. He sat after collecting his fifth foul but the Celtics could not get any closer than 90-78.
Turkoglu helped ice the win with a three-pointer with four minutes to play and then made a jump shot to give the Magic a 17-point lead.
