Eastern-conference leading Boston (57-15) opened its advantage to six games over the idle Detroit Pistons with 10 games left. The Hornets (49-22) had a five-game winning streak halted.
New Orleans, which leads a strongly contested Western Conference, beat Boston 113-106 last Saturday night.
Rajon Rondo added 17 points and Ray Allen had 12.
Chris Paul paced the Hornets with 22 points and 10 assists. Peja Stojakovic had 17 points and David West 14.
Garnett appeared to want his teammates to pick up the intensity defensively midway into the third quarter, and he showed them when he dropped to his knees setting up to cover David West at the top of the key. West did drive by for a basket after Garnett squared up defensively, cutting it to 72-68, but the Celtics scored 19 of the next 24 points over the ensuing 5:56 to move ahead 88-73.
Rondo keyed the decisive spree with consecutive jumpers that ignited a 12-0 run. Boston shot 68 percent in the third, hitting 13 of 19 attempts.
Eddie House nailed back-to-back 3s to push it to 96-78 early in the final quarter. House's jumper from the left corner pushed Boston's lead to 20 points with 7:31 to play.
New Orleans, which shot 60 percent in the second quarter, led 60-56 at the half.
Neither team had more than a six-point lead in the opening quarter that ended with Boston leading 30-24 before the Hornets' bench outplayed the Celtics' reserves during a 13-4 spree that opened the second quarter.
