Isaiah Hicks added 12 points off the bench for the Tar Heels (29-6), who led by just a point after a frustration-filled opening 20 minutes in which the Eagles stayed right with the East Region's top seed. But UNC dominated the opening 10 minutes of the second half, running off a 20-3 burst by controlling the boards and locking down defensively to build a 20-point lead.
That helped the Tar Heels avoid the unwanted history of being the first 1-seed to lose to a 16-seed in tournament history.
Florida Gulf Coast (21-14) already owned a bit of underdog history with its "Dunk City" bunch the first 15-seed to reach the Sweet 16, in 2013.
This would've topped that considering the game was in UNC's home state, were the Tar Heels haven't lost an NCAA game in 37 years. But by the end, this one looked a lot like those other 1-vs-16 matchups, with the Tar Heels just too big, deep and athletic for the Atlantic Sun champions.
Christian Terrell had 15 points to lead Florida Gulf Coast, which shot 60 percent in the first half but went 2 for 15 to open the second half as the Tar Heels finally took control.
By the end of the opening 20 minutes, Florida Gulf Coast trailed just 41-40 to cause a mild wave of concern through the home-state crowd of blue-clad fans filling a rival school's arena.
But the Tar Heels started the second half with a 3-pointer from Marcus Paige, followed by a transition layup from Joel Berry II to restore a cushion. Minutes later, Johnson outfought Eagles defenders for a rebound and scored a stickback while being fouled for a three-point play that suddenly had pushed UNC's lead to eight.
By the time Berry grabbed a loose ball and scored while being fouled for his own three-point play, the Tar Heels led 57-45 with 15:07 left — a margin that would not slip below double digits again.
Florida Gulf Coast: Terrell had seven rebounds and a career high seven assists. . Antravious Simmons had 14 points. . Marc-Eddy Norelia had 10 points and 11 rebounds.
UNC: The 60-percent shooting in the first half was the best in a half against UNC all year. . The Tar Heels improved to 32-1 in NCAA games in their home state, with 28 straight wins since losing in Raleigh in 1979.
UNC advances to Saturday's second round to face the Providence.