They had such an advantage over the Cs in those first two games because they were well-rested, and the Cs had no time to rest or heal up from a grueling second round battle with Washington.
Now that the Cavs have played three games in six days they are in series fatigue and have returned to the same baseline as the Celtics. I doubt there are any blowouts in the next games. The games will be a lot more competitive than games 1 and 2 because the rest advantage the Cavs had is greatly reduced if not eliminated.