Denver Coach George Karl remained stuck on 999 career wins, missing out for the second straight night on a chance for 1,000.
Despite playing without Carmelo Anthony, who sat out the game with knee problems, the Nuggets battled back from an early 19-point deficit and trailed by seven at the break. They managed only two points over the first 4 minutes of the fourth period to lose touch with the Celtics.
Paul Pierce and Kevin Garnett both had 17 points for Boston, Garnett missing just once in nine shots from the field. Glen Davis added 16 off the bench.
Ty Lawson scored 24 in a reserve role to lead the Nuggets. Denver's two straight losses have followed a seven-game winning streak.
Karl is No. 7 on the all-time winning list among NBA coaches. He is attempting to join Don Nelson, Lenny Wilkins, Pat Riley, Jerry Sloan, Phil Jackson and Larry Brown in the 1,000-victory club.
His next chance will come Friday in Toronto.
Reindeer recovered after escaping from Santa during lighting ceremony
Puzzle-maker slips 'Murdoch Is Evil' into Rupert Murdoch's Sunday Telegraph