Marcus Georges-Hunt and Chris Bolden scored 12 points apiece for Georgia Tech (14-11, 4-9).
The Yellow Jackets had won four of seven games since a 79-63 loss at North Carolina on Jan. 23.
North Carolina center Joel James missed his third straight game with a concussion. James' injury helped open the way for coach Roy Williams to move to a four-guard lineup and shortened rotation.
The quick North Carolina lineup caused matchup problems for the Yellow Jackets.
"When they played at that pace, they played it much more under control than when we played it at that pace," Gregory said. "I'll put that as gently as I can."
Williams said the 6-foot-9 McAdoo's defense on opposing centers has helped the Tar Heels keep the four guards on the floor.
"He's had some big challenges the last three games with the guys he's trying to guard," Williams said of McAdoo. "He's done a nice job."
The Tar Heels kept their lead in double figures the final 13 minutes despite shooting only 37.9 percent from the field (25 of 66) for the game.
North Carolina committed only nine turnovers — 10 fewer than Georgia Tech.
"Nine turnovers, I'll take that every game," said Williams, who wore a blue plaid jacket.
"We can't afford to shoot 38 percent and win very often."
P.J. Hairston, who scored a career-high 29 points while making six 3-pointers in the Tar Heels' win over Virginia Saturday, opened the game with another 3. North Carolina then missed its next five shots during Georgia Tech's 8-0 run.
The Yellow Jackets led 19-16 following a basket by Georges-Hunt.
A three-point play by McAdoo started a string of seven unanswered points for the Tar Heels.
Georgia Tech missed each of its six free throws in the first half, matching the margin of its 36-30 deficit.