Williams is making his 21st straight NCAA Tournament appearance with his Tar Heels earning the fourth seed in the West and a matchup against No. 13 seed Harvard.
The Tar Heels (24-11) had the Atlantic Coast Conference championship within reach before a couple of turnovers set Notre Dame loose on a game-turning run.
Harvard (22-7) defeated Yale in the one-game Ivy League playoff for a fourth consecutive NCAA Tournament berth. The Crimson are the first Ivy League team to reach four straight NCAA Tournaments since Princeton from 1989-92.