Boston has won 10 straight for the second time this season, accomplishing a feat the storied franchise hadn't since the 1985-86 season when it went on to win one of its 17 NBA titles.
The defending champions are an NBA-best 39-9 thanks to the current run and a franchise-record 19-game winning streak early in the season.
Detroit's Allen Iverson scored 19 points, moving past Hall of Famer Charles Barkley and into 16th place on the NBA's career scoring list.
Boston jumped out to a 12-4 lead and then scored eight of the first nine points after halftime, providing cushions that proved to be the difference.
The Pistons rallied in the second and fourth quarters and got within three midway through the final quarter, but Garnett's jumper capped a 10-2 run that gave the Celtics an 11-point lead.
Rodney Stuckey scored 19, reserve Richard Hamilton had 14 points and Rasheed Wallace added 12 for the Pistons, who have lost three straight at home and nine of their last 13 overall.
In a rematch of the Eastern Conference finals, tempers flared with 5:56 left in the game.
Boston's Kendrick Perkins was ejected after being called for a flagrant foul following a video review that showed he knocked Jason Maxiell down to the court with a hard foul across the back of his neck.
Maxiell responded with a shove and was called for a technical.
After the game was stopped for free throws, Hamilton made a shot to make it 71-67. Then, the Celtics scored seven straight points to seal the victory.
Notes@: Boston was without F Brian Scalabrine (concussion) and doesn't know when he will return. ... Hamilton played after irritating his groin injury in the previous game. ... The Pistons have wins against five of the NBA's six division leaders, beating the Western Conference's top teams on the road, but are 0-3 against Boston. ... Iverson moved past Barkley in the first half with his ninth point. Only Phoenix's Shaquille O'Neal has more points among active players.
