The Mariners warmed up for next weekend's Johnstone's Paint Trophy Final with a fine performance, soaking up pressure from lowly Mansfield and then breaking to score in each half.
The Stags though will be rueing a remarkable spell of five chances in one minute shortly after their second-half equaliser which could have ended a terrible run of ten defeats in 11 matches at Field Mill.
New signings Kevin Horlock and Neil Wainwright were on the bench for the home side as caretaker boss Paul Holland kept the side which won a week earlier at Bradford City - looking for a victory to secure the job on a full-time basis.
And in the second minute they almost got the perfect start, Nathan Arnold curling a drive narrowly wide. Then Micky Boulding's shot on the turn was saved by Phil Barnes.
At the other end Paul Bolland's powerful strike was turned away by the diving Jason White.
The Stags, playing attractive, passing football, twice opened up the Grimsby defence, but failed to find the vital touch inside the penalty area.
First Boulding just failed to head in a John Mullins cross from the byline and then Matt Hamshaw and Boulding combined well before Arnold fired tamely wide.
A diving Robert Atkinson header cleared the danger from another byline cross, this time from Hamshaw.
But Grimsby grew in confidence as the first half wore on, creating chances before Peter Till blasted in through a crowd of players in the 32nd minute.
The diving Alex John-Baptiste headed Hamshaw's cross over the bar from close range five minutes later as the Stags pressed for a quick equaliser.
Grimsby, still dangerous on the break, should have doubled their advantage in first-half stoppage time, but Danny North blazed over after an error by Stephen Dawson.
Four minutes into the second half the Stags finally turned their pressure into a goal, Arnold collecting Jonathon D'Laryea's pass, turning Tom Newey and firing across the keeper and into the bottom corner of the net.
Three minutes later the Stags went close to taking the lead in an amazing scramble. Arnold's shot was turned away for a corner and from the flag kick Mullins saw two headers cleared off the line by Danny Boshell.
Hamshaw's curling shot was then tipped away by keeper Barnes and from the second corner Mullins headed narrowly over.
Grimsby hit back and Till hit the side-netting when he should have scored as the chances came thick and fast at both ends. Arnold then blazed high and wide from close range for the home side.
Substitute Wainwright, signed 24 hours earlier, saw his free-kick deflected wide as Mansfield poured forward in search of a winner.
But it was Wainwright who allowed Till to run past him and set up Boshell to restore Grimsby's lead with a fine 20-yard clipped drive from the edge of the area in the 74th minute.
Deep in stoppage time, Mullins almost scrambled a second Stags equaliser, but Barnes came to Town's rescue, saving at the foot of the post.