Johnson was key in UNC's second-half production. After managing just two points on one shot attempt in the first half, the 6-foot-9 junior went 5 for 5 after the break - including three straight baskets in the first 90 seconds of the half - and finished with 11 rebounds.
By the final horn, UNC had the best shooting percentage and scoring total allowed all season by Syracuse (14-7, 5-3).
Marcus Paige finished with 22 points, six rebounds and eight assists to lead the Tar Heels, who won despite committing a season-high 20 turnovers that led to 21 points for Syracuse.
Trevor Cooney matched his season high with 28 points to lead the Orange, while Rakeem Christmas had 22 points and 12 rebounds. But Syracuse couldn't keep up with UNC's offense after halftime once the Tar Heels started protecting the ball, finishing at 43 percent shooting in the first trip to Chapel Hill for Hall of Fame coach Jim Boeheim and the Orange.
Syracuse led by six midway through the second half before the Tar Heels finally pushed ahead, going in front for good on Britt's 3 near the 8-minute mark.
UNC led 74-72 before using an 8-1 run to finally build a cushion, getting a tip-in from Johnson and two free throws from Paige for an 82-73 lead with 1:32 left.
Syracuse: Michael Gbinije had 16 points and Tyler Roberson 13. ... Cooney scored 15 points in the first 13 minutes, but cooled off and finished 4 for 13 from 3-point range. ... No opponent had shot better than 48 percent or scored more than 83 points against Syracuse this season.
North Carolina: Kennedy Meeks scored 17 points, 11 after halftime. ... UNC finished with a 42-27 rebounding advantage and scored 16 second-chance points.
North Carolina travels to No. 10 Louisville on Saturday.