Boise State (4-0) is off to its best start since the 1998-99 season.
With last season's Big Sky defensive player of the year, Glen Dean, sitting out with a bruised hand, the Eagles struggled to slow Boise State's fast-paced offensive attack.
The Eagles stayed close early before Westly Perryman and Arnold sparked a 12-5 run late in the first half to give the Broncos a 43-27 halftime lead.
Moritz and Perryman led another 12-5 run to help the Broncos build a 55-33 lead midway through the second half.
Perryman also had four steals and three assists.