Eddie House scored 10 of his 13 points in the fourth, while Rasheed Wallace, who sat out Boston's 106-90 victory over Toronto on Wednesday night because of a sore right ankle, returned to score five points.
Paul Pierce shot 1 for 4 and finished with two points in 26 minutes.
Allen said one of the replacement referees expressed his surprise at Boston's level of intensity in a preseason game.
"I was like 'this is a dress rehearsal but you've got to get it right,' Allen said. "We want to get it right and we want to be perfect in preseason games, regardless of who is on the floor and regardless of who we're playing against. You don't want to have to be trying to figure it out when the real stuff starts."
Boston (5-1) has not lost since dropping a 96-90 decision at Houston on Oct. 7. The Celtics will wrap up the preseason with games Tuesday night at New York and Wednesday night at Cleveland, then open the regular season at Cleveland on Oct. 27.
"We're going to play Tuesday pretty good," Boston coach Doc Rivers said. "Wednesday we're going to really throttle back."
Garnett, who missed last season's playoffs following right knee surgery, said he's ready to get the regular season started right now.
"I wish it started a little earlier," Garnett said. "The more preseason games you play, the more incidents, accidents, all of the above can happen. Five or six, this is where we need to be."
Hedo Turkoglu scored 16 points for Toronto, and Chris Bosh had 15 points and eight rebounds. The Raptors have lost three straight and five of seven in the preseason, but coach Jay Triano isn't concerned.
"It is really 0-0," Triano said of his team's record. "These don't count after one more."
Toronto concludes its preseason with an Oct. 23 against Minnesota, in Sioux Falls, SD, then opens the regular season at home against Cleveland on Oct. 28.
Raptors center Andrea Bargnani scored 13 points before fouling out with 45 seconds left in the third. Bargnani played 21 minutes.
Allen had 12 points and Garnett added 11 in the first quarter to help Boston take a 33-23 lead. The pair spent most of the second quarter on the bench, allowing Toronto to cut it to 54-49 at the half.
Allen went 6 for 6 and scored 14 points in the first half, but missed his first three shots in the third quarter. The rest of the Celtics also went cold, failing to score until Bosh was called for goaltending on a shot by Kendrick Perkins at 7:27. Toronto tied it at 54-all but couldn't take the lead, and the Celtics took a 73-63 lead into the fourth.
"There was a couple of shots that I missed starting the third that I hated I missed because they were dead-on," Allen said. "As a shooter, you can never stop working at trying to make that next shot, being in good shape to make that next shot."
Toronto guard Marcus Banks missed the game because of flu-like symptoms, while forward Reggie Evans (left foot) wasn't in uniform. Swingman Antoine Wright (right knee) took part in a walk-through and shooting drills Saturday, but has yet to make his debut for Toronto.