United's short trip across the Derbyshire border didn't go to plan on Saturday lunchtime.
Goal from Jimmy Ryan, Gary Roberts and Eoin Doyle saw Chesterfield race into a 3-0 lead before Marc McNulty and Neill Collins netted what proved to just be consolation goals.
Two first half red cards - for Michael Higdon and Chesterfield goalkeeper Tommy Lee - added to the drama and the result could have been different had Georg Margreitter also seen red with the score at 0-0.
Loan signing McCarthy, signed on Friday, started. In total, Clough made three changes with Flynn and Higdon also brought into the starting line-up. Campbell-Ryce was on the bench.
Chesterfield were the faster out of the blocks and had won a corner before Jones fired over from distance on four minutes. Skipper Doyle was first in the book, for clattering Morsy, but the early attacking prowess of United caused problems.
On 12 minutes Higdon lost his marker and turned home Wallace's cross but was adjudged offside and home defender Margreitter could consider himself lucky that the colour of the card shown to him was yellow and not red when he crudely halted Murphy's progress towards goal. He was Chesterfield's last defender.
With less than 25 minutes gone, Scougall was the third name in the referee's book, he took one for the team by fouling Ryan, who was to have his moment soon after. With the next attack, Johnson and O'Shea were involved before the latter laid off and RYAN unleashed a first-time drive past Howard's right hand to give Chesterfield the lead.
It didn't get any better for the Blades before the half hour mark when the referee's cards were out again on 29 minutes - this time it was a red for Higdon for a foul on Jones.
A period of reorganisation saw the Blades attempt to contain the home side - Ryan fired over - but the entertainment continued. On 40 minutes, from Evatt's chest back, Flynn beat Lee to the ball and was subsequently upended by the Chesterfield goalkeeper, who became the second to be shown a red card. The resulting free-kick, from Murphy, struck the wall, and there was still more action before the break.
Just before five added minutes was announced, McCarthy's pass was intercepted and ROBERTS was free on goal and slid the ball beyond Howard, in off the far post.
There was a lot to take in at the half-time break but both managers resisted the temptation to make changes at the start of the second period, although it took just five minutes before Clough replaced Wallace with McNulty. Penalty appeals at both ends were waved away as referee Brown stayed in the thick of the action.
United were seeing a lot of the ball in the second half but Chesterfield's back four held firm and the home side looked dangerous on the break. From a Jones cross, Eoin Doyle's header was blocked on the line by Collins and Morsy curled wide.
Another penalty appeal, this time McNulty going down under Margreitter's challenge, was turned down and Clough's final changes were introducing Campbell-Ryce and Harris for Flynn and McEveley.
Ryan sliced wide as the Blades were caught on the break from a corner and home side were finding space and a third arrived on 73 minutes. A cross from the right saw the ball ricochet around the box before dropping Eoin DOYLE to beat the exposed Howard.
United were gifted a glimmer of hope on 81 minutes when Scougall's overhit pass slipped from the grasp of substitute goalkeeper Wright and McNULTY slotted home
In the remaining minutes, plus four of added time, the Blades added a shade of respectability to the score when COLLINS headed home a Campbell-Ryce free-kick, but a section of the 1,957 Blades fans that made the trip had already left the Proact Stadium before the final whistle signalled a disappointing defeat.
Chesterfield: Lee, Evatt, Darikwa, Ryan, Jones, Johnson, Margreitter, Morsy, O'Shea (Wright 41), Roberts (Clucas 66), E. Doyle (Gnanduillet 75).
Unused: Gardner, Raglan, Boco, Banks.
Blades: Howard, Alcock, Wallace (McNulty 50), Flynn (Campbell-Ryce 63), M. Doyle, Murphy, Scougall, Collins, McEveley (Harris 67), Higdon, McCarthy.
Unused: Basham, Davies, Reed, Turner.