The Mariners produced a shocking performance and were dead and buried by the halftime whistle.
By then they were already four goals behind and even after making half-time changes rarely threatened a Lincoln defence in which skipper Jamie McCombe was outstanding.
Town's star strikers Michael Reddy and Gary Jones failed to manage a shot between them and well before the final whistle hundreds of Town fans were queuing to get out of the ground.
Grimsby's only real threat came in the opening 10 minutes with Justin Whittle and Paul Bolland both firing shots straight at Lincoln keeper Alan Marriott.
The game turned Lincoln's way in the 13th minute when Paul Mayo hurled a long throw into the Grimsby box and Luke Foster's header crept in at the far post.
Grimsby were stunned three minutes later when a long clearance from Marriott found its way to Jamie Forrester and the striker, signed on loan from Bristol Rovers in midweek, lobbed Steve Mildenhall from outside the box.
Eight minutes before the break a superb ball from Forrester put Marvin Robinson in the clear but he was hauled down by Mildenhall. Referee Steve Bennett awarded the spotkick which was smashed into the roof of the net by Paul Mayo.
Lincoln's Francis Green fired against the ball from close in before Grimsby were pulled apart again in the 44th minute. Lee Beevers burst down the right flank and flicked in a low cross for Robinson to tap in.
Grimsby boss Russell Slade carried out his halftime team talk on the pitch using a flip chart brought into the centre circle.
He pulled off both Whittle and Ciaran Toner but it made little difference.
Lincoln continued to create chances and should have scored on the hour when Green beat two defenders only for his final shot to be blocked by the body of Mildenhall.
Foster twice went close before Lincoln wrapped things up six minutes from the end. A dreadful clearance from Gary Croft went straight to Beevers who burst forward before sending in a low shot which deflected off the leg of Ben Futcher past the hapless Mildenhall.