Michael Coulson scored the only goal as Grimsby beat Forest Green.
The forward scored his first of the season after taking advantage of a mistake in the Rovers defence to fire home from the centre of the box.
Liam Hearn and Damian Spencer earlier had chances for the Mariners before Coulson's breakthrough.
Rovers searched for an equaliser but struggled to get behind Town's defence and when they did keeper James McKeown denied Reece Styche and Yan Klukowski.
Forest Green: Bittner, Hodgkiss, Stokes, Turley, Graham, Forbes (Turk 66), Allen (Klukowski 55), Rowe, Norwood, Styche, Griffin (McDonald 56). Subs Not Used: Imudia, Matthews.
Grimsby: McKeown, Wood, Green, Kempson, Pearson, Coulson, Disley, Artus, Makofo (Elding 83), Spencer (Duffy 64), Hearn (Eagle 88).Subs Not Used: Church, I'Anson.
Booked: Artus, Pearson, Coulson, Kempson.
Goals: Coulson 44.
Ref: Peter Banks (Merseyside).