But the match turned on an incident in first-half added time with Grimsby leading through centre-back Nick Fenton's header from a 16th minute corner.
Grimsby winger Peter Beagrie unnecessarily brought down Matty Robson and up stepped Jon Daly to bury the penalty and put Hartlepool level.
After that it was simply one-way traffic. Gary Liddle fired home a free-kick from 25 yards on 52 minutes to put Hartlepool 2-1 ahead.
There was no further scoring until the final six minutes when a back-pass let in Daly on 84 minutes for his second goal and Hartlepool's third.
Then Joel Porter completed the rout in stoppage time with a fine solo effort.
The second half was in complete contrast to an even first period with Hartlepool starting well before being pegged back by Grimsby opener.
Midfielder Ricky Ravenhill hit the post and if that had gone in the home side would have been two goals ahead.
But then came the match-changing incident at the end of the first half from which Hartlepool never looked back.
The patient home fans finally turned on their manager and players with chants of "what a load of rubbish'' as Grimsby simply ran out of ideas and were devoid of any shape.
This was Grimsby's second home defeat after being unbeaten in the league since January and the alarm bells are now clearly ringing for manager Graham Rodger.