James scored 27 points on 12-of-23 shooting while Australian-born guard Irving added 18 to lead seven double-figure Cavalier scorers in Cleveland’s 12th home triumph in a row.
Two days earlier, James criticized himself after missing two pivotal free throws in the final seconds of over-time in a two-point loss to Houston, one in which he missed 20 shots from the field and went 3-for-11 from the free throw line.
The Cavaliers improved to 38-24, trailing Chicago by only percentage points in the fight for the Central division lead, while Boston slid to 23-35, one game behind Brooklyn and Charlotte for the final playoff spot in the Eastern Conference.
Kevin Love and J.R. Smith each scored 12 points for the Cavaliers, who made all 14 of their free throws attempts.
The Celtics, led by 15 points from Brandon Bass, fell behind 61-36 at half-time.
James capped an 11-0 Cleveland run early in the third quarter with a layup to give the Cavs a 76-42 edge and seal Boston’s fate.