Former Grimsby striker Jack Lester netted a brace to help Chesterfield come from two goals down and claim a 2-2 draw at Blundell Park, leaving his former employers deep in the relegation mire.
Lester headed home Ishmel Demontagnac's cross midway through the second half and then gathered a loose ball to fire home in the box 10 minutes later.
Prior to his double, the struggling home side had dominated and deserved their advantage.
Grimsby hit the woodwork early on, Michael Coulson's fizzing low free-kick beating the wall and a standing Tommy Lee in the Chesterfield goal before coming back off the crossbar.
But Lee was beaten when Tommy Wright collected Dean Sinclair's neat pass to slot home the opener after 28 minutes.
Jean-Louis Akpa Akpro doubled the lead when he forced home Mark Hudson's pass on the stretch just before the hour mark.
But the visitors` comeback leaves Grimsby seven points from safety with four games remaining and keeps Chesterfield in the play-off picture.