Mayer got the Redhawks (1-2) going when he found Jack Sorenson on an 18-yard touchdown toss to finish the game-opening eight-play, 93-yard drive.
Early in the second quarter, Camden Orth threw a 24-yard touchdown pass to Derick Eugene to pull the Sharks (0-3) into a 7-7 tie.
But Miami proceeded to establish control of the line of scrimmage and pulled away when Kevin Davis crashed in from 3 yards out with 5:22 remaining before halftime. Five minutes later, Gabbert threw a 16-yard scoring pass to Jalen Walker for a 21-7 lead.
Miami outgained Long Island 523-216 in total yards.
Orth finished 15-for-21 passing for 178 yards.
Lakota West grad David Afari added 78 yards rushing for Miami, which visits Army next Saturday.
SATURDAY’S GAME
Miami at Army, Noon, CBS Sports Network, 980, 1450