It looked like being a promising afternoon for the Spireites when Laurence Maguire headed them in front from Liam Mandeville’s cross after just six minutes.
But two brilliant long-range strikes in four minutes from John McAtee and Gavan Holohan turned the game around midway through the first-half.
Harry Clifton headed a third on 50 minutes and Ryan Taylor secured an emphatic win for the visitors with 12 minutes remaining.
This was Chesterfield’s heaviest defeat in the league this season and they can have no complaints about the result.
Since Paul Cook was appointed they have won just three out of 11 and it is now 27 points chucked away from winning positions in total this campaign.
The manner of the defeat is the most concerning and it is a big wake-up call for them. If they don’t get their act together soon, they could be at risk of throwing this season away altogether. Who would have thought that when they were flying high at the top of the table in January?
This defeat drops them to fifth. They need to dig out a couple of ugly wins and hope those around them slip-up in their games in hand. But, even if they do get over the line into the play-offs, at the moment they are stumbling into them which doesn’t fill you with much confidence.
WHAT WENT WRONG?
This was the Spireites’ worst performance of the season and it came as a result of losing the midfield battle. Cook’s men were second to every loose ball, they didn’t win their individual battles and they got outmuscled.
There was no structure or discipline in the centre of midfield and the Mariners cut them through too easily and too often and could have scored more.
Chesterfield got outworked and outfought and that is very worrying. They were all over the place at times and there was a lack of leadership on the pitch.
Grimsby’s two long-range stunners really knocked the stuffing out of Town and you could see the panic in the ranks. They really needed some calm heads but they were more like headless chickens.
The first two goals were stunners but the third goal, five minutes after half-time, was the worst of the lot and so soft as Clifton ghosted in behind Jeff King to head in. The fourth was another poor goal but you can forgive it because they were chasing the game by that stage.
Up the other end, apart from Maguire’s goal and Manny Oyeleke striking a post, they didn’t threaten that much either with many attacks fizzling out.
Credit to Grimsby, they came for the win and they got what they deserved. Physically they were superior and with the skill of McAtee and the experience of Taylor, they posed a real danger up top.
Cook’s preferred formation may well be 4-2-3-1 but he might have to look at going back to what this squad knows well and that is a three-man defence. A good manager sticks by his principles, but also knows when to adapt when something is not working.
It might mean harshly dropping one of Jamie Grimes or Laurence Maguire, but they’ve got to get Gavin Gunning back in the starting line-up because of his leadership skills.
Oyeleke got 30 minutes under his belt as a second-half substitute after missing the last nine games which is a big plus. If he can, he has to start at Wealdstone on Saturday.
And Danny Rowe, although he was not involved, did join in some of the pre-match warm-up which was a welcome sight after six months out.
Loach; King, Grimes, Maguire, Whittle; Weston, Whelan (Oyeleke, 58); Mandeville, Khan (Quigley, 58), Miller (Rowley, 85); Asante. Unused subs: Gunning, McCourt.