The Cavaliers fell to the defending champion Celtics 112-105.
Donovan Mitchell led all scorers with 31 points and grabbed 10 rebounds for a double-double.
Darius Garland sunk 25 while Jarrett Allen tallied a double-double on 17 points and 18 rebounds.
Cleveland had a four-game winning streak snapped and fell to 40-and-10.
The Cavs visit the Pistons tonight.