I was originally inclined to go with Ray because of the two shots, then I rethought it. Pierce was the Celtics most dominant player, and it was has drive that enabled his pass to Ray, and the defense had to bite on the drive because of how he had been playing in the entire fourth quarter. Pierce could have taken that shot, but he didn't, but his overall play and pass really set up that shot for Ray.
Paul Pierce - 3 (See above)
Ray Allen - 2 (Can words say enough?)
Big Baby - 1 (He kept us alive with the play where he got two o-reb, then knocked down the jumper)