Bruins guard Ian Clark entered shooting better than 46 percent from 3-point range but was 3 of 8 from beyond the arc.
Kerron Johnson led Belmont with 22 points and Clark finished with 21.
Kevin Parrom, Kaleb Tarczewski and Nick Johnson added 12 points each for Arizona, which will play the winner of Harvard-New Mexico.
Michigan 71, South Dakota 56: Glenn Robinson III scored 21 points and Mitch McGary added 13 points and nine rebounds, helping fourth-seeded Michigan overcome a rough night for star Trey Burke.
Burke made only two field goals and left the game briefly in the second half after a hard fall under the basket. The star point guard came back after that, but he finished with only six points.
Michigan (27-7) advanced anyway behind Robinson, McGary and Tim Hardaway Jr., who scored 21 points.
South Dakota State (25-10), the 13th seed, trailed by only four at halftime but couldn’t keep up. High-scoring guard Nate Wolters was held to only 10 points.
Burke was held in single digits for the first time all season.
Michigan plays the winner of VCU against Akron on Saturday.