Kevin Garnett added 19 points and 10 rebounds for the Celtics, who even without the suspended Rajon Rondo won their third straight and finally are playing like the team that has ruled the division for the last half-decade.
The Knicks want that title now, but Carmelo Anthony and his teammates were reminded how tough the Celtics can make it.
Anthony had 20 points but shot 6 of 26 while battling his temper, Garnett and foul trouble. J.R. Smith led the Knicks with 24 points.
Rondo was suspended Monday for making contact with a referee in a game against Atlanta on Saturday and failure to cooperate with an NBA investigation. Without the NBA's assist leader, the Celtics relied on the kind of defense that has been absent too often this season.
They allowed 78 points per game in their last two wins, then held the Knicks to 40 in the second half Monday.
Pierce, who was also in foul trouble in the tightly and sometimes inconsistently called game, put it away with a jumper with 45 seconds to go, blowing a kiss toward the crowd he loves to torment after putting the Celtics up by six.
Anthony had averaged 34.4 points in his last 10 games and had a pair of 40-point performances last week, but his jumper was off from the start Monday as the Knicks had their two-game winning streak snapped.
Boston led by four when Anthony and Garnett became extra physical with each other on a Boston possession that ended with a turnover with 9:03 remaining. Anthony followed him all the way to midcourt as they jawed at each other following the play, leading to technical fouls on both players.
The trash talk didn't just stay on the court -- or between players. Pierce tried to throw the ball in from the sideline shortly after, only to have Spike Lee standing and yelling in his ear the whole time.
Jason Kidd's 3-pointer tied it at 86, but Pierce dunked and Avery Bradley made a jumper for a four-point lead with 5:32 to play. The Knicks got it to one before Pierce's jumper with 3 1/2 minutes to play, and the Knicks never got that close again.
The Celtics have won the last five Atlantic Division titles, starting with their NBA championship season of 2007-08.