At first, it looked like the Boston Celtics had run out of juice. Two straight blowouts on the West Coast, but a quick trip to Arizona seemed to be the end of the line. Shots weren’t falling, despite a good offensive process, and the Phoenix Suns were finding a way to put the ball in the basket. Then, the Celtics flipped a switch. They went on a 50-11 run from midway through the second quarter through late in the third. It was pure dominance. How?