David Reeves hit a hat-trick to snatch a point for Chesterfield.
Glynn Hurst headed Chesterfield into the lead but Iain Anderson equalised from 25 yards and Jamie Lawrence put Grimsby ahead from a quick throw-in.
Reeves put the hosts 3-2 up with a header and a penalty but team-mate Mark Innes was sent off and Darren Barnard curled in Grimsby's third to level.
Isaiah Rankin put Grimsby 4-3 up but Reeves scored another penalty before Town's Darren Mansaram was dismissed.
Chesterfield: Muggleton, Dawson, Blatherwick, Evatt, O'Hare,
Allott, Innes, Niven, Brandon, Hurst, Reeves.
Fullarton, Richmond, N'Toya, Robinson.
Grimsby: Fettis, Crowe, Young, Warhurst, Barnard, Anderson,
Coldicott, Lawrence, Armstrong, Antoine-Curier, Rankin.
Ford, Jevons, Campbell, Thorrington, Mansaram.
Referee: F Stretton (Nottinghamshire)