3. Lack of rebounding.
You cant give up second looks to a team like that. They will skin you alive on threes with second opportunities. The decision to bench sullinger when he was doing such a good job rebounding was an odd one, despite sully struggling with issue #2.
11 offensive rebounds in a game like that isn't a lot.
At one point in the second half (late third or early fourth), the Spurs had 10 offensive rebounds against 20 defensive rebounds for the Celtics. They were pulling down a third of their misses. A large number.
It wasn't until the fourth quarter after San Antonio had already built their 10-11 point lead that Boston started to even up the rebounding numbers.
I think the final box score made it look better than it was for Boston. The Celtics were chasing the game late on and out-rebounded SAS by 6 in final period ... but they never really threatened the Spurs in that final period. The damage was already done. The Celtics fourth quarter rebounding didn't carry much meaning.
IIRC, Terry hoisted up a three down 6 almost halfway through the 4th. He missed, SAS (Parker?) hit a three, Terry missed another, and the lead ballooned from there.
The game was well within reach, and had Terry nailed that open three, the final minutes of the game could have been very different. In what could have been a 3 point game turned into an 11 point game in about 30 seconds. C's basically folded from there.