Bass grabbed six rebounds, Pierce distributed five assists and Kevin Garnett added 12 points with six boards as the Celtics took their second victory in three games.
Bass capped a 14-1 third period run with a two-handed dunk to put the Celtics firmly in control.
Boston currently holds the sixth playoff seed in the Eastern Conference.
Washington got 16 points and 10 assists from John Wall.
Celebrity Families of 2014 [PHOTOS]