The Bulls starting PF was DeRozan, who is 6'6". The Celtics had a starting frontcourt that included Tatum, Horford, and Williams. Not only did the Bulls outrebound them 50-38, but the Celtics didn't really take advantage of any mismatches with their size by posting up down low. Tatum should have had a field day in the paint, and lived at the line as a result (he was 3-4 free throws).