DeMarco was 8-for-14 for 145 yards for the Monarchs (5-2). His first scoring pass was 42 yards to Reid Evans, then he had scoring strikes of 14 and 41 yards to Nick Mayers. DeMarco also had 12 carries for 38 yards
Old Dominion freshman Desmond Williams added a career-high 145 yards on 29 carries with one touchdown, a 1-yard run capping a 16-play, 94-yard drive with 3:51 left.
Campbell (1-5), which lost its fifth straight game, led 10-7 at halftime.
After Jonathan Plisco's 76-yard punt pinned Campbell at its own 1 with 8:52 left in the third quarter, Old Dominion took advantage of the field position to regain the lead.
Daniel Polk was 16 of 23 for 185 yards for the Camels and also rushed 17 times for 70 yards and one touchdown.