Chester City gave a classic away performance to inflict Grimsby's first home defeat of the season.
An experienced and well-drilled Chester side gave Grimsby a lesson in how to take chances and then defend a lead.
Grimsby made it hard for themselves almost from the start when, by failing to play to the whistle, they conceded a tenth-minute opener to Chester.
Grimsby full-back Tom Newey fouled a Chester player out on the touchline and, although the referee's assistant raised his flag, play went on and as Grimsby stopped, Kevin Ellison's cross was easily headed in by John Murphy.
Town to their credit came back well and their striker Isaiah Rankin missed two good chances as Grimsby enjoyed the majority of the first-half play.
They drew level when a good piece of football resulted in a Peter Till cross being headed in from close range by Grimsby man-of-the-match Danny Boshell on 24 minutes.
With the score at 1-1 by half-time it was all to play for in the second half, but Grimsby shot themselves in the foot just two minutes into the second period.
Striker Simon Yeo, a 42nd minute substitute and so often a scourge of Grimsby in the past, thundered a shot against the inside of the post and Ellison coolly ran the ball in the net.
From that point on it was the Grimsby attack against the Chester defence but Grimsby only really carved out two chances.
Sub Andy Taylor should have scored when he was played clear but keeper John Danby stuck out a foot and diverted the ball to safety.
Then with ten minutes left, sub Gary Jones did everything right from a corner only to see his header bounce back into play from the foot of the post.
Chester's impressive away form continues and if they can only sort their home form out they could be challenging for automatic promotion.