Goals from Steve Evans and Chris Llewellyn put them well on top and Matt Done settled it midway through the second half.
Back at his home-town club striker Neil Roberts nearly set-up an early goal when he sent Done away on the left but Mark Jones aimed a weak shot from the cross and gave Phil Barnes an easy save.
A Darren Ferguson corner picked out Evans for a firm header that Peter Beagrie hacked away at the back post and under more pressure from the home side, Ben Futcher cleared over his own crossbar to deny Roberts.
Evans opened the scoring with his first goal for the club heaving in from a Ferguson cross, first turning his marker and leaving Barnes diving too late.
Llewellyn headed the second goal, again set up by Ferguson, whose left-wing cross surprised defenders and again Barnes was left clutching thin air.
All Grimsby could offer in reply were two free-kicks from Tom Newey. Whittle met the first with a tall header that Ingham caught easily and the second from the edge of the area went straight into the keeper's arms.
Another centre from Newey was headed away to Isaiah Rankin whose hasty shot went wide.
An Evans shot gave Barnes a tricky low save and when Llewellyn rounded Newey and fired a left-foot shot he was only inches off target.
Llewellyn set-up the second goal with a brilliant run but when he mis-kicked the ball ran free for Done to hit it first time across the keeper.
The Mariners switched tactics later but without success. The best they could offer was a hopeful drive over the crossbar from Rankin and a shot from Peter Bore which Ingham turned round the post.