The game was marred by a scary neck injury suffered by the Pelicans' Ryan Anderson, the team's leading scorer.
Anderson collided with Boston's Gerald Wallace during the fourth quarter and the game was delayed while doctors worked to determine the seriousness of the injury. Anderson was eventually taken off the court on a stretcher and transported to a nearby hospital.
New Orleans officials said Anderson had feelings in his extremities.
That led to Roberts going to the line and he made both attempts for a three-point lead. Jared Sullinger missed on his long-range shot that would have forced overtime.
Boston was led by Bradley with 22 points. The Celtics lost their third in a row and have dropped six out of seven.