Valentino, who was 14 of 29 passing for 192 yards and one interception, rushed for 58 yards for the Flyers (1-1). Justin Watkins caught seven passes for 97 yards and a touchdown.
Josh Keil's 1-yard touchdown put Robert Morris (0-3) ahead 7-0 less than 4 minutes into the game. Dayton tied the game on Valentino's 8-yard touchdown pass to Justin Millio with 4:49 left in the first half.
The Flyers went up 14-7 on Brian Mack's 2-yard rushing score just before halftime.
After a scoreless third quarter, Valentino connected with Watkins on an 8-yard score to put Dayton ahead 21-7. Camdin Crouse's 25-yard TD pass to Sherrod Evers late in the fourth pulled Robert Morris within the final margin.