The Silkmen fell to a narrow defeat away at Blundell Park as an Ethan Robson strike secured all three points for our hosts.
In a match of few chances for either side, Robson skipped past Jay Harris and into the Macclesfield area before unleashing a fierce strike into the roof of Owen Evans’ net early in the second half.
Grimsby started the better of the two sides, with Ahkeem Rose finding a way into a dangerous position before seeing Miles Welch-Hayes recover well to block his effort.
Macc responded to this early scare through Jay Harris, but his strike from distance was tipped around the post by the outstretched arm of McKeown in the Grimsby net.
Robson came close midway through the first half, but he failed to connect with a header and Owen Evans comfortably saw the ball behind.
The Silkmen grew into the game as the half progressed, with Theo Archibald trying his luck on a number of occasions from just outside the area.
Our best chance of the half came ten minutes before the interval, as some good link up play between Paddy Osadebe and Virgil Gomis almost saw the latter through on goal; but McKeown was alert to the danger and just about claimed the ball ahead of Gomis.
Barely ten minutes after the second period started, Grimsby scored what proved to be the decisive goal as Robson fired home from close in.
Macc almost replied instantly, but Gomis couldn’t quite connect cleanly with a close-range volley and the ball sailed wide of McKeown’s post.
Substitute Max Wright had the best chance of the second half, but he could only strike the post after a well worked Grimsby move.
The Silkmen continued to push for the equaliser with Joe Ironside almost connecting with a Welch-Hayes headed cross, but we could not find a way through as Grimsby held on to secure all three points.