Chesterfield slipped to their first defeat of pre-season, losing 2-1 at the hands of an impressive Alfreton Town side in front of just over 1,000 at the Impact Arena as they were forced to rue a series of missed chances.
Former Mansfield Town striker Nathan Arnold gave the home side the lead moments before the break after rounding Spireites keeper Tommy Lee, but Danny Whitaker hit back for the visitors in the second-half following good work from Craig Westcarr.
But the home side snatched the spoils in the 77th minute when substitute stopper Richard O'Donnell's clearance fell kindly to an Alfreton trialist, who duly punished the visitors.
The Reds proved to be tough opposition for the League Two new boys, although they begin their assault on the Conference National next week against Stockport County, while Sheridan will still have two pre-season tests against Championship opposition to prepare his squad.
Spireites manager Sheridan named a strong side for the short trip to Alfreton, with Lee returning between the posts at the expense of former Sheffield Wednesday keeper O'Donnell.
Drew Talbot, who scored against AFC Telford last time out, was moved to right-back alongside a back-four of Sam Hird, Terrell Forbes and the returning Neal Trotman.
Winger Whitaker retained his place on the right after an impressive display at the New Bucks Head stadium, with former Arsenal schoolboy Marc Randall returning alongside Sam Togwell in the middle of midfield.
Jordan Bowery was preferred as Marc Richards' strike-partner, meaning Westcarr was exiled on the right of midfield and it was the visitors who started brightly and should have taken the lead inside the opening 15 minutes with a series of decent openings.
Bowery showed his presence early on with a burst of pace after Randall's sumptuous ball, but his touch was too heavy and was reeled in the by the home side's goalkeeper.
The pacy frontman was at it again moments later and was unfortunate not to give the Spireites the lead after a scintillating break from Sheridan's men. Randall was predictably at the hub of all things creative as he volleyed an incisive pass to the feet of Richards, who sprayed a wonderful ball out to Whitaker.
He supplied Bowery, whose powerful drive was turned away for a corner. From the ensuing set-piece, the visitors troubled again this time through the returning Trotman but he could only angle his header narrowly over when unmarked from close range.
It was the turn of Richards to go close next when he latched onto a long ball forward, which completely caught the Town back-four square, but the former Port Vale man looped his attempted lob harmlessly over.
And he then let the Conference National side off the hook after just 13 minutes with the best opening of the game so far, when he fired wide from around seven yards with the goal at his mercy.
It was a blistering start from the visitors, but it was only a matter of time before Alfreton got a foothold in the game and their first foray into Chesterfield's box came via striker Arnold, who blazed his shot over after Forbes' cross-field ball for Talbot squirmed free.
The lively striker came close again for the Reds in the 40th minute, when he curled a delicate effort onto the roof of the net with Lee at full-stretch. But just two minutes before the break, the home side made Sheridan's side rue their missed chances when Arnold raced clear of Trotman and rounded the advancing Lee to slide home an undeserved opener.
Sheridan introduced Tendayi Darikwa and Mark Allott for Trotman and Randall respectively after the restart, but the former Mansfield man Arnold continued to cause trouble as he forced Lee into a sprawling stop after showing Hird a clean pair of heels.
The visitors responded shortly after through Westcarr, though, who saw his deflected effort glance the crossbar after exchanging passes with Bowery, before Richards saw his free-kick angle just the wrong side of the far post on the hour-mark.
The lively Bowery was replaced shortly after by Scott Boden and his impact was immediately forthcoming as the pink-booted striker found Westcarr with an intelligent touch, before the former Magpies ace fed Whitaker and he cut inside before picking out the far corner with precision.
The goal was no more than the visitors deserved, but Alfreton almost took the lead again seconds after the restart when right-back Josh Law thumped the woodwork with Lee stranded.
Sheridan then rang the chances, introducing Richard O'Donnell, Craig Clay, Jack Waddle, Jacob Hazell and Jonathan Wafula and with just 13 minutes remaining on the clock, the home side found themselves back in front after the former Sheffield Wednesday stopper cruelly mis-kicked his back-pass and was duly punished.
It was harsh on the Spireites and they could have levelled in the dying seconds when substitute Hazell raced clear, but he was thwarted by the onrushing Town goalkeeper to condemn the League Two side to their first defeat of pre-season.