Drew Windler had 15 points and seven rebounds for the fifth-seeded Bruins (25-9), who will face Robert Morris in the next round. JJ Mann finished with 11 points, shooting a dismal 1-of-8 behind the 3-point line, while Reece Chamberlain added eight assists.
Greg Mays logged 15 points and Kenneth Lowe chipped in 12 off the bench for the fourth-seeded Phoenix (24-7).
Belmont shot 54.3 percent from the field in the opening frame as it led 49-37 at the intermission. Green Bay made 58.3 percent of its field goal tries while taking 11 fewer shots.
The Bruins did not shoot as well in the second period as they converted 37.5 percent of their field goal attempts. The Phoenix connected on 43.5 percent of their shots from the floor, but missed on all seven attempts from 3-point range. The Phoenix could not take advantage of the Bruins' poor shooting, as Belmont outscored Green Bay 31-28 in the half.
Belmont outscored the Phoenix from behind the 3-point line, 30-9, and also forced the hosts into 21 turnovers.