Three minutes after coming on the striker raced clear from the halfway line before firing into the bottom corner to crown a fine Mariners' fight back.
Grimsby, who had lost seven consecutive matches and scored just one goal prior to their hat-trick of victories, looked to be in trouble when their former striker Michael Boulding gave Mansfield the lead.
But the Stags failed to build on their lead and an outstanding save from Grimsby keeper Phil Barnes to deny Mansfield midfielder Stephen Dawson at the start of the second half proved to be the turning point.
The Mariners, roared on by 1,400 travelling fans, made the better start in a low key opening with Tom Newey's near-post cross forcing Jason White into a save.
Then Paul Bolland tried his luck from 20 yards, but the keeper comfortably gathered his low drive.
The Stags, despite several neat interchanges of passes, were unable to carve out an early chance of their own and should have fallen behind in the 18th minute when Nick Fenton's flying header from a Danny Boshell corner landed on the roof of the net.
The scare at last inspired the home side and within 60 seconds Barry Conlon saw his dipping shot just clear the bar.
But there was no denying the Stags in the 30th minute when Conlon turned goal provider, crossing from the right for Boulding to pounce at the second attempt.
The striker's first close-range shot was charged down, but the ball broke kindly for him to roll the rebound wide of the stranded keeper Barnes.
Conlon thought he had added a second soon after, but his close range header from a Stephen Dawson cross was ruled out for offside.
Grimsby almost levelled after a spell of pressure. Fenton's fierce 20-yard drive crashing into the side netting with keeper White beaten.
But the visitors did equalise three minutes before half-time when Bolland raced into space at the far post to convert a Newey cross, despite the efforts of the diving White who touched Bolland's effort onto the post before the ball bounced over the line.
The start to the second half was as scrappy as the beginning of the first period, although Bolland saw his 25-yard drive rise narrowly over the bar as the Mariners looked to complete the turnaround.
At the other end Barnes dived to punch away a Hamshaw cross as the Stags began to take control and then the wingman's surge into the area was followed by a crisp shot which grazed the outside of the post.
The Grimsby keeper repeated his heroics to turn away Dawson's pile driver after a sweeping cross-field passing move, but from then on the Mariners took over.
Ciaran Toner blazed well wide from 20 yards, Boshell thundered a 20-yard volley inches past the post, Bolland weaved his way past three defenders before shooting straight at White, and Newey's speculative 30-yard shot swerved into the side netting.
The Stags, restricted to rare breakaways in the final stages, were unlucky when Conlon's glancing header flew over from a Hamshaw corner, but North's late winner ended their hopes of a first win in three games.