Both of these factors would seem to be more a function of personnel than any sort of strategic shortcomings. While this particular performance by Irving was of a different variety from most of the other epic performances that the Sixers have allowed to opposing guards this season — Jimmy Butler’s on-the-ball defense down the stretch was about as good as you could hope for in such a situation — but the fact remains that this team will struggle to get where it is going if it does not improve its defense on the perimeter. That the Sixers had an open look at the buzzer in regulation for the win should not obscure the meticulous way in which the Celtics' starting unit used its size/strength advantage to generate open looks throughout the first two quarters. By halftime, three different players had backed J.J. Redick down and sank fadeaway jumpers over the veteran guard, a strategy that played a big role in the 57-51 lead that the Celtics built.