They dominated large chunks of their crucial clash against Sawley but ultimately lost by 25 runs.
This was their fourth defeat in five Division One games, a lean run which could not have come at a worse stage of the season. A failure to press home an advantage, particularly in the field, has been a recurring theme in Chesterfield's recent performances. It was apparent again here.
Sawley looked in trouble when, having won the toss, they were reduced to 41-5.
Brothers Tom and Harry Wanford claimed the first three wickets before Muhammad Zaroob struck twice in his first over. When Zaroob (4-31) trapped Muhammad Atif leg-before, the visitors were 67-6.
But then the initiative was wrenched firmly away from Chesterfield. Aidan Meyer and Carl Cruz played themselves in carefully before upping the tempo dramatically.
Chesterfield switched to defensive field placings but the Sawley duo repeatedly hit the ball through or over them as they raced to a century stand in only 14 overs.
Cruz eventually holed out to mid-off for 55 off the bowling of Reece Johnson but Meyer powered on. He hit some mighty blows and finished 101 not out as Sawley were bowled out for 223, a far higher total than had seemed likely two hours previously.
The start of the Chesterfield run-chase was hectic. There were nine scoring strokes - all fours - in the first five overs during which both openers were dismissed.
But a third-wicket stand of 122 between Zaroob and Alex Hibbert looked to have put Chesterfield firmly back on track.
They appeared in little trouble with Zaroob striking several powerful shots and the left-handed Hibbert played with increasing fluency and authority.
On 156-2, Chesterfield looked strong favourites. But then Zaroob (78) was beaten and bowled by a well-flighted delivery from off-spinner Josh Glover and the innings went into freefall.
Glover took a wicket in each of five successive overs - including Hibbert for 58 - and Meyer struck twice in one over with his wrist-spin.
Glover finished the match by having James La Brooy lbw, giving him figures of 6-39.
Chesterfield were all out for 198, having lost their last eight wickets for 42.
They stay fourth in the table but, with only one game left - at Langley Mill United on Saturday - can no longer catch Sawley in the second promotion spot.
However, the Seconds could still be promoted if they win their final Division Four North match following a two-wicket victory at Hollinsend Methodist.
They restricted the home side to 176-7 off 45 overs with James Taylor taking 3-40.
Opener Michael Michailidis (46) put Chesterfield on course before Simon Westwell made 40 and Ben Jenkins steered them over the line with 20 not out.
They need to beat Langley Mill at Queen's Park on Saturday and hope Belper Meadows take fewer than nine points from their match at Ilkeston Rutland.
The third team suffered a three-run defeat against Butterley United in Division 10 North.
Alfie Woodhouse took 5-31 as they bowled out the visitors for 172 but they fell agonisingly short in the run chase.
They are away to Ashover Barbarians on Saturday.
Ali Dixon's 130 led the Sunday side to 299-6 off 40 overs in their Mansfield & District League match at Farnsfield.
But the Premier Section clash was abandoned as a draw with the hosts on 116-7.
The Sunday side finish their campaign this weekend against Welbeck at Queen's Park.