Celtics Hub looks at some stats for the Celtics in "clutch" situations. See details here.
Here's a sample analysis.
You can tell immediately that the Celtics offense is just about as efficient in the “clutch” as it is otherwise–pretty damn efficient. They don’t shoot the ball as well from the floor, but they make up for it by getting to the line more often (and hitting the FTs) and taking better care of the ball. This is nothing earth-shattering, but it’s something of a validation of Doc’s late-game coaching and proof that the C’s have evolved from the “throw the ball to Pierce and stand around” crunch time strategy.