AFC Wimbledon made the League Two play-offs and Grimsby missed out as the visitors won at Blundell Park.
Sam Hutchinson's second-half goal was enough to give Johnnie Jackson's side the three points and extend their season in the play-offs.
The Mariners were the team that needed to win more, and they were pushing for the opener early on, with skipper Danny Rose heading just wide as he got on the end of Kieran Green's delivery.
Wimbledon did not have a shot on target in the first half, but they were happy to slow the game and bunker down for a draw that would secure their play-off spot.
The visitors came out with greater intensity after the break, and Hutchinson found the breakthrough in the 53rd minute from a rebound effort.
Marcus Browne ran through on goal past the hour mark with a great chance to double Wimbledon's lead, but he blasted wide with his shot across goal.
Justin Obikwu tested Owen Goodman late on, but the away side held on for a season-defining victory.
Report supplied by PA Media.
