A messy goal ten minutes from time condemned Spireites to a defeat that saw them return to the foot of the table.
Sub Gavin Mahon slid the ball through the middle where both David Davis and Neal Trotman were unable to block it.
The ball then slipped to another replacement, Jonathan Forte. The ex-Blade rolled the ball beyond Tommy Lee for the 80th-minute winner to register new manager Keith Curle’s second win in four days.
Chesterfield had looked set for a decent point after being the better side in the second half following a turgid opening 45.
Boss John Sheridan had been forced into making changes following the win over Sheffield Wednesday. His two most regular starters of the season, Mark Allott and Drew Talbot, had both picked up knocks last weekend, Simon Ford’s knee and Gregor Robertson’s hamstring kept them out while Nicky Ajose dropped to the bench.
That meant Jimmy Juan was brought back in after a calf injury but, after a great start, he soon had to be replaced after falling awkwardly and twisting an ankle.
Craig Westcarr, against his last club, Jamie Lowry and Dean Morgan were less surprising starters but, at right-back, the most unexpected name on the teamsheet was that of Tendayi Darikwa.
The 20-year-old Nottingham lad had previously made only a couple of sub appearances in cup competitions. He’d been on loan at Conference North side Hinckley United but was recalled early to make his league debut and he didn’t let anyone down.
Lee’s double save to deny the Hughes, Lee and Jeff, was the first half’s major moment and straight from the restart the game burst into life.
Alan Judge, who after County’s goal struck the bar, saw Lee tip a shot behind for a corner that started the action. From that flag-kick, the Spireites broke clear. Morgan fed sub Jordan Bowery who ran on goal but saw Stuart Nelson save in a one-on-one that the striker should have won.
David Davis, a solid battler throughout and Westcarr saw shots blocked as the Spireites moved up a notch, Lowry’s free-kick was saved and Westcarr almost took advantage of some terrible communication in County’s defence.
Nelson made a fine save to block a Jack Lester rocket and Davis almost nipped in at a corner before County brought on Ben Burgess. In the immediate aftermath of the change, the hosts scored.
A Trotman header came closest to finding the net for Chesterfield whose second-half performance, up to the late goal, had been ahead of their opponents.
Sheridan said: “I thought the second-half performance was really good. I made a lot of changes because of injuries and I tried to get a balance.”
COUNTY (4-5-1): Nelson 6, Freeman 6, Edwards 7, Chilvers 5, Harley 5, Judge 8, Montano 7 (Forte 59, 7), Bishop 7, Bencherif 6 (Mahon 71, 6), J.Hughes 7, L. Hughes 6 (Burgess 79). Subs (not used): Mitchell, Stewart.
Chesterfield (4-4-2): Lee 7, Darikwa 6, Trotman 6, Thompson 6, Ridehalgh 6, Westcarr 6, Juan 7 (Bowery 32, 6), Davis 8, Lowry 6, Lester 6, Morgan 6 (Ajose 81). Subs (not used): Fleming, Whitaker, Smith.
Goal: Forte 80.
Ref: Paul Tierney (Lancs).
Bookings: Trotman (Chesterfield); Harley (Notts).