Duke never trailed, shot 51 percent - 57 percent in the second half - and dominated the ACC's best team on the glass, outrebounding North Carolina 34-20.
Marcus Paige - who led UNC's second-half comeback two weeks ago - finished this one with 24 points, while Brice Johnson had 15 and James Michael McAdoo added 13 for the Tar Heels (23-8, 13-5).
They shot nearly 60 percent but couldn't overcome their disadvantage on the glass and are locked into the No. 4 seed in the league tournament.
Leslie McDonald added 12 points for North Carolina, which was denied its fourth win over a top-five team, but briefly made things tense in the final minutes when Paige converted a four-point play to make it 81-73 with 2:50 left.
But the Tar Heels' point guard missed 3s on the next two possessions - with Parker blocking the second of those with 2½ minutes left.
Quinn Cook hit two free throws, Amile Jefferson added another and Parker hit two foul shots with 2:03 left to push the lead to 86-73 and effectively end it.
Cook finished with 11 points and Rasheed Sulaimon added 10.