Harrell, a junior transfer from the University of Virginia in the ACC, hit 10-17 field goals, 6-10 three-pointers and 3-3 foul shots as the Tigers improved their record to 6-3.
The Tigers led 23-22 with 4:41 left in the first period before finishing the half outscoring the Eagles 14-2.
"We just made a run and it all starts with defense," Harrell said. "We know our identity now and we try to bring it (good defense) every time we play."
Coach Tony Barbee agreed with Harrell's assessment of what the Tigers did well to take a solid lead in the contest. "That is what sparked our run was our defense," he said. "We just keep talking about it.
"In that last four minutes is when we got some separation when we got some stops and got in transition," the coach added. "It is really hard to get in transition if you don't get stops."
Auburn's two other starting guards scored in double figures with senior Chris Denson finishing with 15 points and freshman Tajh Shamsid-Deen adding 14. Denson struggled with his shooting, hitting just 4-14 field goals, while Shamsid-Deen made 5-7 of his seven shots and was 2-3 on treys.
Shamsid-Deen committed just two turnovers in 31 minutes of action at point guard.
Boston College star guard Olivier Hanlan led the Eagles with 28 points as he got hot in the second half. He helped the visitors cut a 20-point Auburn lead to 61-53 with 6:04 left in the game, but the Tigers made the plays needed in the final minutes to preserve the victory.
"They are a tough team," Barbee said of Boston College, which fell to 4-8 on the season. "They have played an incredibly tough schedule. We knew that they were going to be desperate to get a win here before the break. I am just proud of the way our guys started and finished because we did a lot great things.
"Defensively, keeping them in relative check (7-23 on treys) off the three-point line was big," Barbee said. "That is a key for their team. They shoot and make a lot of threes and I thought we guarded the three-point line very well.
"We made our free throws, which was big--77 percent," Barbee pointed out. "Our assist-to-turnover ratio was positive. We played for each other out there on the floor the entire time."
Commenting on Harrell's big game, the coach said, "K.T. was big. I have been waiting for the breakout. He has been playing well all year. Heck, he is averaging 18 points per game, but he has probably had our or five nights when he had these type of games in front of him.
"K.T. is a guy who struggles sometimes with self-confidence and I have been on him about that to keep going, to keep fighting, keep pushing and keep being aggressive and tonight he was that," Barbee pointed out.
The Auburn coach also had praise for Shamsid-Deen. "Tajh did a great job. They came at him a little bit trying to trap him. He did a great job of orchestrating against the press when we switched up our press attack and had him take it out (Inbounds throw in) and get it back to him. He did a great job of running the team against a very talented and experienced guard."
For the game Auburn shot 48.1 percent and hit 17-22 free throws while Boston College shot 43.5 percent and hit 20-29 free throws.
Stat of the Game: Auburn made 10-22 three-point shots, a season-high for the Tigers.
Worth Noting, Part 1: The Tigers turned the ball over just seven times despite Boston College pressing much of the second half.
Worth Noting, Part 2: There was a second half delay due to a malfunctioning shot clock. The Tigers led 58-47 at that point with 9:39 left to play. The crew at Auburn Arena replaced the entire goal/backboard to solve the problem.
Halftime Numbers: Auburn led 37-24 at the break thanks to good defense and better shooting. The Tigers made 8-14 three-pointers in the period with Harrell hitting 4-5 attempts and Shamsid-Deen making 2-3. The Tigers shot 54.2 percent from the field while holding BC to 42.1 percent. Harrell led the Tigers with 16 points. AU out-rebounded the Eagles 13-12 in the half and forced eight turnovers while committing five. No Auburn player had more than one foul in the half.
Boston College coach Steve Donahue had these comments on his team's performance. "We came out and didn't play well from the start. I give Auburn credit. They stayed with it and really played well, especially in the first half.
"I give our team a lot of credit," Donahue said. "We came back in the second half, competed and got the deficit down to single digits. It seemed like every time we had a wide-open shot, we couldn't make it in. The same goes with foul shots and layups. We just shot ourselves in the foot.
"I give Auburn a lot of credit," the coach added. "I thought they played well. Their past games they got beat pretty badly, and have played two really good last games."
Auburn returns on Dec. 30th with a 7 p.m. home game vs. Arkansas-Pine Bluff.