Danny Boshell bagged two penalties as Grimsby eased past Chesterfield to stretch their unbeaten run to 10 games.
Boshell hit the first from the spot after keeper Barry Roche felled Danny North and North's close-range shot after a Kevin Gray blunder made it 2-0.
Nick Hegarty hammered in the Mariners' third from Peter Till's cross.
A Kevin Cooper shot and a neat Jamie Ward finish set up a tense finish but Boshell netted his second spot-kick after Roche bundled over Gary Jones.
Grimsby: Barnes, Atkinson, Fenton, Newey, Hird (Bennett 88), Hegarty, Hunt, Boshell, Clarke, Till (Jones 78), North (Bore 90).
Subs Not Used: Montgomery, Bolland.
Goals: Boshell 19 pen, North 31, Hegarty 53, Boshell 86 pen.
Chesterfield: Roche, Moloney (Ward 55), Kovacs, Gray, O'Hare (Fletcher 46), Lowry, Niven, Leven, Robertson, Smith (Cooper 55), Lester.
Subs Not Used: Downes, Picken.
Booked: Roche, Kovacs.
Goals: Cooper 73, Ward 83.
Ref: M Russell (St Albans).