The Celtics’ lack of defensive execution Tuesday night against the Miami Heat came as no surprise, because their adaptation to Doc Rivers’s adjusted system was spotty at best during the preseason.

While the Celtics hardly emphasized winning during exhibition games, they played defense consistently in only one — the nationally televised win over the Brooklyn Nets Oct. 16 when they were responding to losing their first three games against NBA teams, including a 32-point pasting by the Philadelphia 76ers.