Mangum, a junior college transfer, shot 12 of 15 from the floor. Brandon Nazione scored 14 points to go along with 11 rebounds for his second double-double this season.
The Eagles (2-1) were 31 of 59 from the floor for 52.5 percent, better than their free-throw percentage of 51.9 (14 of 27).
The Saints (3-3), an NAIA team, had no one score in double figures, making just 13 of 61 shots for 21.3 percent, including 2 of 22 from 3-point range. They turned the ball over 25 times, 15 coming on steals.
The Saints held a 7-6 lead before being outscored 33-5 the rest of the half as the Eagles took a 39-12 lead at the break. Eastern Michigan scored the first 15 points of the second half.