Drew Talbot and Derek Niven broke Grimsby's spirited resistance before Ryan Bennett pulled one back for the visitors.
Niven's 75th minute goal was particularly sweet because the midfielder only returned to the squad at the end of January, after recovering from testicular cancer.
His first goal since he was diagnosed with the illness brought the home crowd to its feet, but Grimsby gave Chesterfield some anxious moments late on and will have a good chance of retaining their league status if they show the spirit and commitment they displayed in this match.
They will need to be sharper in front of goal because it was missed opportunities at the start of the game that proved costly.
Jean-Louis Akpa-Akpro had an excellent game but he should have done better in the fourth minute when Nick Hegarty put him in on the right but his low shot was pushed behind for a corner by Tommy Lee.
It was Hegarty who wasted the next opening in the 12th minute when the ball dropped invitingly in front of him 12 yards out but his volley went wide.
Chesterfield gradually exerted a measure of control and Jamie Lowry fired over before former Grimsby striker Jack Lester hit the inside of the right-hand post in the 36th minute.
Chesterfield struck the woodwork for a second time ten minutes into the second-half, Talbot's lob from 25 yards going in off the underside of the crossbar.
Grimsby made two substitutions but it was Chesterfield who scored again in the 75th minute, when the ball was picked up by Niven on the right-hand edge of the area and he unleashed a shot into the top corner.
It was a superb effort but Grimsby replied instantly when Danny Boshell swung over a corner and Bennett drove a low shot through a crowded six-yard box.
Grimsby might have levelled minutes later when Jamie Clarke sliced a volley off target and Grimsby never gave up but Chesterfield held on to leave the visitors in the relegation zone of League Two.