Rashard Lewis had 28 points and Hedo Turkoglu scored 24 for Orlando, which played without starting point guard Rafer Alston, who was suspended by the NBA for slapping Eddie House in the back of the head in Game 2.
Paul Pierce broke out of his slump to score 27 points, and Rajon Rondo added 15 for the Celtics, who trimmed a 20-point deficit to seven before the Magic regained control.
"You give them their inside game and their outside game, then you don't have a chance," Pierce said.
Game 4 is tomorrow in Orlando.
Howard had four blocks in the first half, forcing the Celtics to become a jumpshooting team much like the Magic did to win Game 1. On the first play of the second quarter, Howard soared so high he had to brace his left hand against the backboard so he wouldn't smack his head while swatting Stephon Marbury's layup attempt into the stands.
It was no different on offense.
Howard sprinted down the middle of the lane to take a pass zipped from the wing by J.J. Redick, gripping the ball with two hands for a thunderous dunk that gave Orlando a 43-31 lead. The Magic would eventually go ahead by 14 points in the period.
"Our defense was awful. They made every shot," Celtics coach Doc Rivers said. "I thought they were the aggressors and we were the retaliators all night."
The Magic took a 20-point lead early in the third quarter before Howard picked up his fourth foul, and the Celtics ended the period on a 12-2 run capped by a breakaway dunk by Rondo to cut the lead to nine points after three periods. The Celtics trimmed the deficit to seven in the fourth quarter, but the Magic regained control of the game to pull away late in the final period.
In another game:
* At Houston, Kobe Bryant scored 33 points, leading all five starters in double figures as the Los Angeles Lakers beat the Rockets, 108-94, in Game 3 of their Western Conference semifinal. The Lakers hold a 2-1 advantage in the best-of-seven series; Game 4 is tomorrow. Ron Artest's 25 led Houston, which also got 19 points and 14 rebounds from Yao Ming.
* Washington Wizards forward Antawn Jamison had surgery on Thursday to remove a bone spur from his right ankle. The two-time All-Star is expected to make a full recovery.
* The University of Louisville insists there is no truth to a Yahoo! Sports report that said Rick Pitino had inquired about the vacant Sacramento Kings' coaching position. Pitino was reportedly in his office yesterday but did not feel it necessary to address the situation.
* Attorneys for former 76er Jayson Williams say they'll seek to have his convictions for covering up a fatal shooting thrown out on grounds of racial bias. Attorney Joseph Hayden said in court in Somerville, N.J., yesterday that he will seek a new trial based on a racial slur used by a former employee of the Hunterdon County Prosecutor's Office. *