Williams, who missed nine games after rolling his ankle during a Nov. 15 game against Charlotte, also dished off seven assists for Brooklyn, which won at home for the first time in seven games.
Brook Lopez helped out with 24 points and Alan Anderson added 15.
Avery Bradley's 22 points led the Celtics, whose win streak ended at three.
2014: NFL Cheerleaders [PHOTOS]
UPI Sports Results for September 19, 2014