It was Grimsby's seventh successive defeat but this should not deter from a marvellous display by Peterborough who were briefly threatened when Town pulled a goal back midway through the half to make it 2-1.
But Posh simply moved up a gear and added two more goals to run out convincing winners.
The first two goals were scored by leading marksman Aaron McLean who had two chances but stuck them both away.
He converted a Tom Williams cross on 32 minutes and then scored his second four minutes into the second half when the impressive Craig Mackail-Smith found him in space and he put the ball beyond keeper Phil Barnes.
Grimsby switched to three men up front and sub Martin Butler neatly hooked the ball in on 63 minutes after Danny North had nodded forward.
But Peterborough roared back and McLean set up Mackail-Smith for the third goal even though the Grimsby keeper got his hand to the ball.
Both sides continued to push forward and sub Scott Rendell hammered the final nail in Grimsby's coffin minutes after he had replaced McLean.
That was the end of the scoring although both sides had earlier hit the woodwork from free-kicks.
First midfielder Dean Keates struck the Grimsby bar and then Town midfielder Jamie Clarke did the same at the other end.
But there was simply no stopping rampant Peterborough who were roared on throughout by over 1,200 travelling supporters.
For Grimsby, who at one time harboured play-off hopes of their own, the season rapidly becoming an embarrassment and this was their fourth successive home defeat.