Rochdale ended a run of three defeats with a smash and grab 1-0 victory at Grimsby thanks to Grant Holt's late strike at Blundell Park.
Playing a rigid 4-5-1 formation they defended well and scored a splendid winner with 10 minutes remaining.
A long clearance from keeper Neil Edwards beat everybody but Rochdale striker Holt who got the better of Grimsby skipper Justin Whittle and beat keeper Anthony Williams with a fine volley.
Grimsby tried desperately to get back into the game and substitute Chris Williams hit the top of the bar in the dying seconds.
After their recent bad run Rochdale made their intentions clear and their stifling and smothering tactics gave Grimsby little scope to create much in front of goal.
It might have been different if midfielder Terry Fleming's well-placed shot had gone just inside the post instead of being well saved by Edwards but, that save apart, the Rochdale keeper had an easy 90 minutes.
So bad was the game that the highlight for Grimsby fans was the introduction before kick-off of several members of the 1971-72 fourth division championship team and manager Lawrie McMenemy.
That was as good as it got as Grimsby surrendered their unbeaten home record in disappointing fashion.
The pressure is mounting on the Mariners as they need to maintain their previous good home form having lost their first three away games of the campaign.
For Rochdale it was a welcome win - only their third of the season and much-needed after their alarming 3-0 home defeat by neighbours Bury.
Grimsby need to pick themselves up quickly but face a tough visit to Macclesfield next Saturday while Rochdale will be looking to build on this victory.