Grimsby survived a late Wrexham fight back to climb above the Welsh side with their first win in five matches.
The Wrexham defence failed to clear a corner adequately, the ball sloppily allowed to fall to Steven Watt who fired through Chris Maxwell's legs.
After the break a poor Chris Blackburn clearance fell to the prolific Alan Connell who made no mistake.
Curtis Obeng set up Nathaniel Knight-Percival for a short-range headed goal in injury time, but it was too late.
The defeat ended an eight-match unbeaten run for the Dragons.
Grimsby: O'Donnell, Bore, Kempson, Watt (Garner 49), Ridley, Wood, Wright (Hudson 81), Cummins, Eagle, Carlton (Peacock 75), Connell.
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Subs Not Used: Croudson, Gobern.
Booked: Eagle.
Goals: Watt 17, Connell 65.
Wrexham: Maxwell, Blackburn, Sinclair, Andrews, Ashton (Obeng 57), Tolley, Keates, Harris (Knight-Percival 26), Taylor, Mangan, Morrell (Cieslewicz 50).
Subs Not Used: Brown, Pogba.
Booked: Harris, Obeng.
Goals: Knight-Percival 90.
Att: 2,532
Ref: Paul Davison (Cleveland).
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