Chicago (58-20), winners of 17 of their last 19 games, closed out the third quarter with an 11-4 run to pull away from the Celtics (54-24).
"This meant a lot because you're going against a team you could see in the playoffs," Bulls guard Derrick Rose said after scoring a game-high 30 points.
"You don't want those teams to have confidence. We were aggressive. That's the way it's going to be. We're a tough team. We grind wins out."
The Bulls allowed the Celtics just four field goals in the fourth quarter and, with just four games remaining, Chicago look like genuine title contenders.
"I just thought they were far more physical, tougher, more prepared, which is on me," said Celtics coach Doc Rivers. "I thought Thibs (Chicao coach Tom Thibodeau) did a better job.
"I thought (Carlos) Boozer did a better job, I thought Derrick Rose did a better job. I just thought overall they just competed far better than us tonight."
MVP candidate Rose added eight assists for the Bulls and Luol Deng scored 18 of his 23 points in the second half.