Most of this math is way beyond me (ok, all of it is), but thankfully stat nerds like Tom Ziller are here to help me with my homework.
Boston's defense held Miami's offense to an efficiency almost nine points per 100 possessions lower than normal in the first round, and saw Cleveland's offensive efficiency dip 7.5 points per 100 possessions. Orlando's offense scored 9.5 points more per 100 possessions than Charlotte had normally given up, and a whopping 20 points more than Atlanta had typically allowed.
But in Game 1, Orlando was slowed. The Magic's offense has its first "loss" of the postseason, with the Boston defense performing 8 points per 100 possession better than usual. The Magic's offense was 16 points per 100 possessions worse than usual, a Boston defensive effort comparable to the Celtics' best nights against Cleveland and Miami.
There are also pretty graphs over there that seem to be solving the world's economic crisis, or showing me how to avoid traffic on my commute. Regardless, it all boils down to the Celtics playing dominant defense. More of that please.