Southport substitute Darren Stephenson scored three minutes from time in a dour contest against Grimsby.
A forgettable first half saw one chance of note when the ball fell to Louie Soares on the half volley but his shot flew high over the bar.
The second half was equally short of entertainment until Stephenson, on loan from Bradford, took aim from 25 yards.
His shot flew into the bottom left corner for Southport's 13th away win of the season.
VIEWS FROM THE DRESSING ROOM:
Grimsby Town joint-manager Paul Hurst told BBC Radio Humberside:
"Second-half it turned out to be exactly what it was, an end of season game. I hate to see that and it's not what we asked but there was no energy, no tempo to the game from either team.
"We didn't find that decisive pass or decisive cross. Conditions where difficult in terms of the crossing a little but I thought we passed it really well up until that final third. It was just that bit of creativity or a bit of individual brilliance to create a goalscoring opportunity.
"We certainly feel that we're better than where we've ended up but ultimately the saying goes the table doesn't lie after forty-six games."