Keon Moore, Andre Smith and Joab Jerome had 14 apiece for Winthrop (18-12). The Eagles made all 21 of their free throws and hit 8 of 22 from 3-point range. Jerome made all nine of his free throws, Johnson made three 3-pointers and Moore had eight rebounds.
The game was knotted at 51 with 7:52 left. Then Johnson hit back-to-back 3-pointers to start a 10-2 run to pull away. Moore's free throws at the 1:33 mark gave Winthrop its first double-digit lead of the game.
Winthrop moves on to play top-seeded High Point in the quarterfinals on Friday.