San Diego quarterback Grant Sergent completed 19 of 26 passes for 262 yards and threw three touchdowns. Isaiah Williams ran 19 times for 109 yards and scored two touchdowns.
Dayton trailed 27-3 when Cole Dow scored on a 20-yard run with 3:34 left in the second quarter.
Dayton faced a 33-10 halftime deficit when Sergent threw a 4-yard touchdown pass to Isaiah Smith in the final minute of the first half.
Dayton rallied in the second half. Dow threw a 15-yard touchdown pass to Alec Keathley with 10:15 left in the third quarter. Then early in the fourth, Dow ran one yard for a touchdown run. Dante Casciola threw a two-point conversion pass to Gavin Lochow to cut San Diego’s lead to 33-25.
That was as close as Dayton got. San Diego clinched the victory when Eric Haney intercepted Dow and returned it 22 yards for a touchdown with 3:16 left in the fourth.
It was the third interception of the game for Dow, who completed 4 of 9 passes for 76 yards. Casciola completed 6 of 15 passes for 56 yards.
Dayton returns to action at 1 p.m. Saturday against St. Thomas (2-2, 1-0) at Welcome Stadium. St. Thomas beat Morehead State 35-28 on Saturday.