Brentford were handed another home defeat at a wet and windy Griffin Park as a Gary Jones goal early in the second half settled the game in Grimsby Town's favour.
The Bees battled gamely, created a number of openings and were hit by a sucker punch of a goal by the visitors in the 57th minute.
The hosts made a very bright start and could have been ahead early on, Ryan Dickson brought a fine low save from Phil Barnes with a dipping left footed effort and Charlie Ide headed the resulting corner wide.
Gary Smith shot into the side netting as Brentford continued to press and Ross Montague headed narrowly over before Alan Connell volleyed over the top.
Grimsby's three-man midfield were unable to deal with the work-rate of Smith and Kevin O'Connor, playing his 300th Brentford game, and they created nothing until midway through the half.
Their first half chance fell to Danny North, who shot wide on the stretch and Simon Brown had to be out of his goal quickly to dispossess the same player soon after.
But Brentford will still well on top, Connell had a header deflected with and Montague was unfortunate to divert a shot from Smith wide when it looked set for the back of the net.
Grimsby's clearest opening fell to North late in the half when he ended a nice move, involving at least half a dozen players and more than 15 passes, by snatching at a shot from 14 yards and shooting wide.
Brentford came within a whisker of taking the lead minutes later when Montague met a Ben Starosta cross, the ball hit the post and was eventually scrambled away off his line by Barnes.
And The Bees ended the half like they started it, in the ascendency, Montague had a shot blocked and Dickson brought another save from Barnes with a dipping free kick.
Grimsby made a bright start to the second half Paul Bolland shot wide and Nick Hegarty had an effort held by Brown before the Brentford goalkeeper made a fine save from a James Hunt header and Karleigh Osborne had to be alert to clear a Nick Fenton header off the line from the resulting corner.
Montague had another effort blocked by Ryan Bennett after a nice run by Starosta, who was testing the Grimsby back line with his attacking runs, but The Mariners went straight up the other end and took the lead.
North was the architect with a fine run, which took him to the by-line on the right hand side, and he picked out Jones with a neat pass, he took a touch and drilled it low past Brown.
Brentford tried to respond; Starosta tested Barnes with a shot from distance and then almost set up O'Connor for an equaliser with a cross that was a little too strong.
Hunt could have wrapped the game up with a header from a Sam Hird cross, but he could only nod it straight into the ground and Brentford cleared.
The Bees continued to press, dominating possession and territory but unable to create the clear-cut chance they needed.
Substitute Lee Thorpe had a header saved and right at the death Thorpe and Connell were unable to force the ball home from inside the six yard box after Matthew Heywood drilled the ball across.
Brentford: Brown; Starosta, Heywood, Osborne, Charles; Ide (sub Shakes 80 mins), O'Connor, Smith (sub Moore 88 mins), Dickson; Connell, Montague (sub Thorpe 73 mins)
Subs (not used): Masters, Poole
Grimsby Town: Barnes; Atkinson, Bennett, Fenton; Hird, Hunt (sub Whittle 90 mins), Bolland, Toner, Hegarty; Jones, North (sub Rankin 80 mins)
Subs (not used): Montgomery, Boshell, Butler
Bookings: Bolland (31 mins), Toner (90 mins)
Attendance: 3,999 (335)
Written by Chris Wickham