Grimsby survived a second-half fightback from 10-man MK Dons to triumph at Stadium MK.
Goals from Kieran Green, Jaze Kabia and Charles Vernam gave the visitors a 3-0 first-half lead, with the Dons also seeing Jon Mellish sent off.
George McEachran's own goal and Connor Lemonheigh-Evans gave MK Dons hope, but the Mariners held out.
Grimsby took the lead when Green turned in Vernam's cross in the ninth minute.
Moments after being denied by Craig MacGillivray, Kabia made it 2-0 in the 23rd minute when he converted the rebound after the goalkeeper had spilled Vernam's effort.
Vernam added the third just before the half-hour mark as his crisp strike from outside the box found the top corner.
Dons defender Mellish was dismissed in the 36th minute for catching Kabia with a high boot, but the hosts scored just after half-time when McEachran turned Marvin Ekpiteta's cross into his own net.
Lemonheigh-Evans rifled home from Callum Paterson's long throw in stoppage time, with Jack Sanders missing a chance to equalise with the final kick.
Report supplied by PA Media.
