BOSTON – Lose another key player, win once again.

It’s not a trend the Boston Celtics want to continue much longer.

The Celtics responded to yet another blow to their lineup with a 97-84 victory Friday night against the reeling Orlando Magic, getting double-doubles from Paul Pierce and Kevin Garnett in winning their third straight.

Boston lost point guard Rajon Rondo at the beginning of the week to a torn knee ligament and learned Friday that rookie Jared Sullinger is also out for the season following back surgery.

“He was playing great,” Coach Doc Rivers said of Sullinger. “The good news is we know he can play and he will be a very good player. In the long run this will make him healthier.”

“Losing Rondo was big enough and now we’re losing Sully, one of the best rebounders on the team,” guard Courtney Lee said. “It was definitely shocking. We didn’t know how serious (his) injury was when he left the game.”

Rivers told his team after Friday morning’s shootaround that Sullinger would be out for the season.

“(It was) one of those moments where it’s, ‘Man, it can’t get much worse than this,’ ” said Lee. “We want to stay positive. We need to continue to fight and continue to push.”

“With the injuries, a number of guys are stepping up and that’s what we are going to need,” said Pierce, who had 14 points, 11 rebounds and seven assists, then sat out the fourth quarter.

Garnett added 14 points and 10 rebounds, Jeff Green scored 17, and Courtney Lee had 14 points and five assists for the Celtics.

“The production is coming from everybody,” said Lee, who inherited Rondo’s job at point guard. “Rondo, he’s our playmaker. He’s racked up a lot of assists with his playmaking. Now we have to move the ball and make sure we’re in the right spots to execute the offense.”

The Celtics had assists on 30 of their 42 field goals while shooting exactly 50 percent. Jason Terry and Leandro Barbosa scored 12 each for the Celtics, who had six players in double figures.

“We have to be a team by committee,” Rivers said. “I’m asking guys to play different spots. It does create confusion on the other end.”

It helped that the Celtics were facing Orlando, which last won Jan. 16 and has been dealing with injury problems that rival those of the Celtics. The Magic were without their top two scorers in Aaron Afflalo (calf) and Glen Davis (broken left foot), then lost point guard Jameer Nelson to a bruised left forearm.

“It’s part of basketball and we’ll continue to deal with it,” Coach Jacque Vaughn said. “It means other guys have to fill in and fill roles.”

Nelson, who averages 7.4 assists and is third on the team in scoring at 15.3 points per game, didn’t play in the second half.

“I took an elbow to the forearm so we’ll see how I feel (Saturday),” he said.

J.J. Redick had 15 points and five assists, and Nikola Vucevic had 14 points and 14 rebounds to lead the Magic, who finished with 95 shots.

Only 36 of them went in and hardly any midway through the second half.

“We got some good looks. The ball just didn’t go in,” Vaughn said.

The depleted Magic still managed to push the Celtics through much of the game, taking advantage of 15 turnovers and shaky free-throw shooting; Boston went 9 of 14 from the foul line.

Orlando had been chipping away at the lead in the third quarter, pulling to 57-54 on E’Twaun Moore’s three-point play with 5:04 left in the period. Boston slowly rebuilt the lead with a few short runs, then broke open the game in the fourth when the weary Magic wilted defensively.

“They made shots, went on a little run and we couldn’t answer back,” Vaughn said.

Pierce scored the last four points of the third quarter, putting the Celtics up 72-59 and starting a 10-0 run for Boston. The Celtics opened the fourth quarter 7 of 9, including a series of dunks by Lee and Green during an 8-2 spurt that extended the lead to 86-63.

Andrew Nicholson had 14 points and 10 rebounds, and Moore also scored 14 for the Magic.

NOTES: Boston has won seven straight regular-season games against the Magic. Boston had 30 assists. The Magic were 1 of 13 on 3-pointers in the first half. Orlando hasn’t won since beating Indiana on Jan. 16.