Amherst, MA -- (Sports Network) - Lou Williams poured in a game-high 27 points on 7-of-12 shooting from the field and the Philadelphia 76ers toppled the defending NBA-champion Boston Celtics, 98-92, in the first preseason game for both teams at the Mullins Center, home to UMass basketball.

Williams went 12-for-13 from the charity stripe, including several in the waning moments to clinch the win. Thaddeus Young scored 21 points on 10-of-19 shooting for the Sixers, who also got 11 points from Elton Brand in his debut with the team. The 6-foot-8, power forward signed a lucrative free agent deal with Philadelphia in the offseason after opting out of the final year of his contract with the Los Angeles Clippers.

Leon Powe led all Celtic players with 12 points while Tony Allen had 11. Patrick O'Bryant and Eddie House contributed 10 points apiece.

The Celtics' "big three" played somewhat sparingly, with each member logging less than 18 minutes. Ray Allen led the way with nine points, while Kevin Garnett and Paul Pierce each hit three shots from the field, including two three-pointers from Pierce.

Boston led by 10 at halftime, 54-44, but Philadelphia cut that lead to 75-72 after three quarters. The Sixers then took the lead late in the fourth on buckets from Williams and Royal Ivey with under a minute to play and held on for the win.