The game was over as a contest in effect when central defender Alan White flashed a header home from a corner and the Quakers added number two on 25 minutes through Gregg Blundell, who shot home at the second attempt.
Grimsby, who brought on two substitutes in the first half, went for broke with a third switch at the start of the second half, but they went further behind on 50 minutes.
Striker Richie Foran had time to steady himself and smash the ball into the roof of the net from close range to make it 3-0.
With a three-goal lead, Darlington sat back and allowed Grimsby to come at them but, despite playing a bit better, the Mariners were unable to trouble Quakers keeper David Stockdale.
With men committed forward in a vain bid for a consolation goal, midfielder Michael Cummins caught keeper Gary Montgomery off his line and headed over him in stoppage time.
That was the signal for many of the small crowd to head for the exits and those who were left roundly booed their players off the field at the final whistle.
One very disturbing fact for the home side came when skipper James Hunt was substituted on 26 minutes and, with his face looking like thunder, went straight off down the tunnel, without looking at the dugout.
So the Mariners, with just one home win all season, are now staring relegation full in the face and they still look shell-shocked after heading out of the FA Cup on Saturday.
Darlington's first goal, on three minutes, was the hammer-blow from which Town never recovered and, although the visitors looked a good side, that was not difficult playing against such a poor Grimsby side.