Mullins connected on 4-of-5 attempts from 3-point range while Ramon Sessions -- who finished with 19 points -- drained a jump shot late in the contest, putting the Bobcats ahead to stay.
Kevin Garnett supplied 16 points and 13 rebounds for the Celtics, whose seven-game winning streak was snapped.
Paul Pierce chipped in with 13 points, eight rebounds and eight assists for Boston.
Rosie O'Donnell unveils nearly 50-pound weight loss
Putin thinks Obama would save him if he were drowning