Pierce scored 28 points and became just the third Celtic to score 20,000 points while playing their entire career for Boston. Pierce went 11-of-11 from the foul line.
Ray Allen added 23 points and six rebounds for the Celtics, who have won three in a row. Rajon Rondo ended with 17 points, 15 assists, and eight boards, while Glen Davis tallied 14 points off the bench for the victors.
Andrew Bogut scored 21 points and pulled down 13 rebounds for the Bucks, who are off to a 1-4 start. Carlos Delfino and Ersan Ilyasova each had 15 points.