CHICAGO -- The pregame speech came from an unexpected source, but the motivational message that reverberated throughout the Boston Celtics' locker room could not have come at a more pivotal time.

Via phone, former Boston star Kevin Garnett told the Celtics to "just let go and have fun" as a means to avoid a third straight playoff loss to the Chicago Bulls on Friday night.

The message came across loud and clear.

Al Horford scored 18 points and Isaiah Thomas and Jae Crowder each had 16 to pace the Celtics to a 104-87 victory over the Bulls in Game 3 of their Eastern Conference playoff series. The Celtics still trail 2-1 in the best-of-seven series.

Game 4 is Sunday back at the United Center.

"That was our only goal for this game was (to) just get the win no matter what for us to have a chance to make it a series," Crowder said. "You go down 0-3 and it's really, really tough for you to fight back, but we just want to take it one game at a time and get this game and give ourselves a chance."

Four Boston starters reached double figures. Avery Bradley scored 15 points and Terry Rozier finished with 11 off the bench to round out the balanced scoring attack.

The Celtics jumped on the Bulls early and led by as many as 20 points in the second quarter. But after the Bulls got to within a point early in the third quarter, Boston broke the game open behind back-to-back Thomas 3-point field goals to push the lead back to double figures.

Boston hit the gas pedal and never looked back.

"It's a game of runs," Horford said. "For us, in the first two games, we didn't handle it well when they went on a run. Tonight, we were more composed and handled it much better."

As the Celtics made improvements following back-to-back losses back in Boston, the Bulls struggled without injured Rajon Rondo. Rondo is out indefinitely with a fractured right thumb and will be in a cast for another week before the fracture is re-evaluated.

His absence was noticeable as the start as Chicago -- which got 18 points from Dwyane Wade and 14 from Jimmy Butler -- struggled to play with the pace they had in the first two games of the series with Rondo at the point.

Butler struggled from the field on 7-of-21 shooting, and after nearly drawing even early in the third quarter, the Bulls never recovered when the Celtics took off.

Afterward, Wade said the Bulls simply weren't good enough defensively and couldn't blame the loss on Rondo's injury.

"Just like every injury, every blow, it hurts the team in the moment, but we have to move past it," Wade said. "We have to figure out a way with our young point guards and other guys on this roster to just be better next game."

Robin Lopez finished with 12 points and Nikola Mirotic had 11 for the Bulls, who also got 10 points from Paul Zipser off the bench.

The Celtics maintained their lead by hitting 17 3-point field goals. But the Celtics also kept the ball moving, which the Bulls struggled to stop defensively. Boston finished the win with 34 assists on 41 field goals in the lopsided victory.

Despite the win, Celtics coach Brad Stevens said his team needs a better effort in Game 4.

"I thought we got a lot of good contributions from a lot of guys," Stevens said. "I think we all know that we have to play better on Sunday if we hope to have a chance to win."

NOTES: A day after Celtics coach Brad Stevens hinted at lineup changes, F Gerald Green started for Amir Johnson with Stevens citing Green's shooting ability, length and athleticism. ... G Isaiah Thomas was "feeling better" after traveling to Spokane, Wash., to visit his family after Thomas' sister, Chyna, was killed in a car accident last weekend. "It's been a hard week, he's had his ups and downs," Stevens said. "I think going to Seattle was a good thing, but it was hard." ... Bulls G Rajon Rondo is out indefinitely after an X-ray revealed Rondo suffered a fracture in his right thumb. Rondo will wear a cast to stabilize a previous wrist injury and will be re-evaluated next week when the cast is removed. The injury was initially believed to be a bruise. "It was a shock when we got the call (Thursday) night," Bulls coach Fred Hoiberg said. Jerian Grant started in Rondo's place.