McAdoo scored 12 points in the second half and finished with eight rebounds as the Tar Heels ended Long Beach State's 23-game home winning streak in front of a record crowd of 6,912 at the Walter Pyramid.
The Tar Heels (3-0) got hot from 3-point range during an 18-6 run midway through the second half to pull away. P.J. Hairston had 14 points in a reserve role and Brice Johnson came off the bench and had 10 points and seven rebounds.
James Ennis led the 49ers (1-2) with 18 points and Mike Caffey scored 14. Dan Jennings had nine points and 11 rebounds.
Long Beach State twice pulled to 10 points down in the second half, once on a three-point play by Ennis, but Paige made a pull-up jumper and Hairston hit a 3-pointer for a 73-60 edge.
McAdoo helped extend the lead when he drove and finished with a reverse dunk for a 66-50 lead that made the visiting Tar Heels fans erupt, and he hit a short jumper for a 68-52 lead.
North Carolina went 10 for 27 from 3-point range. Its 27 attempts were as many as it attempted in its first two games.
Hairston, Reggie Bullock, Leslie McDonald and made consecutive 3-pointers for a 59-45 lead. Peter Pappageorge stopped the run with a 3-pointer before Hairston responded with another 3.
North Carolina ended the first half on an 8-3 run and took a 33-32 lead into halftime despite going nearly five minutes without making a field goal late in the first half.
McAdoo and Brice Johnson put back missed shots and Johnson got open for a dunk to pull the Tar Heels to 32-31. With fewer than 10 seconds remaining Johnson took an in-bounds pass and scored an uncontested layup to give North Carolina the lead.
North Carolina failed to make a field goal from McAdoo's put back at 6:50 to his dunk at 2:05. Long Beach State took a 29-25 lead on a corner 3-pointer by Pappageorge to excite the crowd. Caffey scored a floater for a six-point lead before North Carolina overcame two turnovers and a foul to climb back.
The Tar Heels shot only 32 percent in the first half, including 3 for 13 from 3-point range. McAdoo didn't score his first basket until 8:12 to go in the first half. Long Beach State was equally poor with 36 percent shooting and 3 for 14 from beyond the 3-point arc.
Caffey played 38 minutes and Ennis 37 as Long Beach is struggling to find adequate backcourt help after freshman Branford Jones went out with a leg injury.
Long Beach State installed temporary bleachers this season to increase the Pyramid's capacity by 1,800. The previous record attendance was 5,649. North Carolina was the second-highest ranked team to play in the arena behind fourth-ranked Stanford in 2000.