Arias, the only Big Sky quarterback to throw for multiple touchdowns in every game, was 30-of-50 with no interceptions.
Finney had a pair of 1-yard runs for touchdowns in the first half as the Bengals (4-3, 2-1 Big Sky) built a 35-21 advantage.
Ammon Olsen tossed 2-yards to Mitch Jessop to get Southern Utah within a touchdown, 35-28, in the third quarter. The Bengals answered with two Arias fourth-quarter touchdown passes - 29 yards to KW Williams and 43 yards to Josh Cook - and a 42-yard touchdown run from Finney.
Olson was 38 of 65 for 528 yards and three touchdowns, including a 79-yarder to Chris Robinson in the first quarter, to lead Southern Utah (1-7, 1-3).