BOSTON — By the time Avery Bradley, who is recovering from a dislocated shoulder, sank a free throw to give the Boston Celtics a 37-point lead early in the third quarter, Paul Pierce was done for the night, riding a stationary bicycle under the stands and trying to keep his sore left knee from stiffening up. Ray Allen went to the bench soon after to rest his ailing right ankle. He grabbed a seat near Kevin Garnett, who is about to turn 36 and played 42 minutes in the previous game — surpassing 50,000 total minutes in the regular season and playoffs in his 17-year NBA career.