The Cavaliers, the top seed in the East Region, trailed by 10 in the first half and five at halftime to the 16th-seeded Chanticleers before pushing ahead for good with about 9 minutes left.
A No. 16 seed has never beaten a No. 1 since the tournament expanded to 64 teams in 1985, and the Cavs (29-6) ensured history would wait at least another year.
Evan Nolte came off the bench and hit two huge 3-pointers to help Virginia finally push away from the Big South champion Chanticleers (21-13), who were in the tournament for the first time in 21 years.
The game was tied at 47 before Nolte's 3s powered a 23-7 spurt that finally put the game away.
In many ways, the second half was a perfect illustration of the formula that carried the Cavaliers to their first Atlantic Coast Conference tournament since 1976 and the program's first No. 1 seed since the days of Ralph Sampson.
After struggling to slow the hot-shooting Chanticleers early, the Cavaliers locked down on defense while improving their own offensive efficiency to slowly take control.
Virginia shot 65 percent (13 for 20) after halftime— including 6 for 10 from 3-point range — while holding Coastal Carolina to just 32 percent (8 for 25).
Malcolm Brogdon scored 10 of his 14 points after halftime, but the Cavaliers got some of their biggest contributions from the bench.
Gill followed his big three-game run through the ACC tournament by going 7 for 10 from the field to lead Virginia. Meanwhile, Nolte — a 6-foot-8 sophomore who had barely played in recent games — came off the bench after Akil Mitchell picked up his third foul at the 8:53 mark and knocked down the two 3s that helped Virginia push ahead 56-48. He hadn't attempted a shot Friday night before burying those two 3s.