And while their 2-1 win at Saltergate might have been rather streaky, there was no denying the Mariners on their home turf.
It was simply their best performance of the season and, at 3-0 ahead on 53 minutes, it looked game all over.
But Chesterfield had other ideas, and subs Kevin Cooper on 73 minutes and Jamie Ward ten minutes later, gave the visitors hope.
Steve Fletcher then hit the post before Grimsby broke away to earn a penalty.
Chesterfield keeper Barry Roche conceded his second penalty of the match and midfielder Danny Boshell made no mistake.
Right from the start Grimsby meant business as they looked to extend their unbeaten run to double figures.
They could have gone ahead well before the 19th minute when they did eventually break the deadlock.
Striker Danny North, who scored both goals in that earlier victory at Saltergate, was brought down by Roche and Boshell made no mistake from the spot.
Then, on 31 minutes, a terrible mix-up between Roche and central defender Kevin Gray saw the defender head back towards goal and, although the ball was going in, North made sure.
When Grimsby went 3-0 up, with wing-back Nick Hegarty converting a Peter Till cross eight minutes after the re-start, it looked all over.
But Chesterfield, who had brought on Fletcher for the second half, made their last two substitutions just after Grimsby's third goal and it gave them some heart.
Firstly Cooper shot the ball through keeper Paul Barnes' hands and then former Grimsby player Jack Lester set up sub Ward for the second goal.
Grimsby then had a let-off when the visitors struck the post before Boshell wrapped things up from the spot near the end.