A brace by Padraig Amond and a cool Jon-Paul Pittman strike had given the Mariners a 3-0 half time lead, before Omar Bogle's opportunist effort sealed the win in the second half.
Town boss Paul Hurst used the game to give all of his squad a run-out - including youngsters Joe Crowther and Ben Sibbick.
Town first half: McKeown; Tait, Sunter, Gowling, East; Clifton, Brown, Disley, Wright; Pittman, Amond
Town second half: McKeown; Crowther, Pearson, Nsiala, Sibbick; Mackreth, Clay, Venney, Marshall; Bogle, Arnold.
1100 fans watched the game