Chesterfield took advantage of an early second-half red card for Grimsby goalkeeper Christy Pym to win a close game 1-0 at Blundell Park.
Pym was shown a straight red for a last-man challenge on Lee Bonis, and Harvey Rodgers' own goal was enough to secure victory for the Spireites.
An Even, Goalless Opening
Chesterfield keeper Zach Hemming was first to be tested, doing well to stop Jaze Kabia's first-time effort from just outside the six-yard box.