Nathan Tyson became the first substitute in Chesterfield history to score a hat-trick as the Notts County loanee won the game for the home side.
From off the bench, Tyson dealt the knockout blow to leave Fleet on the ropes as the last half hour became a difficult watch for the 126 travelling fans.
Kevin Watson made one change, Gozie Ugwu joining his fellow former Spireite Jermaine McGlashan on the bench, to be replaced by Tomi Adeloye. And Michael Timlin was finally able to pull on a red shirt but had to settle for a place alongside Ugwu and McGlashan in the dugout.
A relatively nervy start considering what was at stake for both sides – or perhaps more an inability to breach either defence – was the order of the day in a first half that lacked any real bite.
The opening action was notable only for a head injury to Ayo Obileye on two minutes and that troubled him sufficiently to result in his replacement by Jamie Grimes on 16 minutes.
In between that, Chesterfield looked purposeful without ever threatening David Gregory’s goal. Lanky frontman Tom Denton was naturally an aerial threat and the home side’s wide men patrolled the flanks to good effect.
Gregory was on hand to save from the head of Denton on 20 minutes but most of Chesterfield’s attacks broke down with the final ball that was either scuffed wide or blocked by a Fleet body.
At the other end, Andre Blackman tried to dig out a couple of crosses for Adeloye and a few set pieces were sent into the box but there was little reason for goalkeeper Shwan Jalal to get his shorts dirty.
The last 10 minutes of the first half livened things up a touch. Adeloye just failed to get anything on John Goddard’s delivery before Jonathan Smith skimmed David Buchanan’s cross just wide for Chesterfield.
Liam Mandeville had sight of goal as he was put through inside the box on 37 minutes but it was another that went off target. And that was Chesterfield’s weakness in those minutes before the break as they fashioned more chances but sent them begging, Gregory saving from Mike Fondop and then Denton heading wide.
The home side had signalled their intent in those moments before the break but for a quarter of an hour after it, they failed to establish superiority.
They still went close, however, and Fleet needed Josh Payne to steer away efforts by Mandeville and Will Evans following a corner.
The visitors had strong claims for a penalty after that when Goddard advanced and Wilson was bundled over and Haydn Hollis was then yellow-carded for felling Wilson moments later.
But with the introduction of Tyson for Fondop on 57 minutes, the game swung Chesterfield’s way. Within three minutes of coming on, Tyson had broken the deadlock, Denton’s header flicked on to the substitute who turned and hammered the ball into the roof of the net.
Fleet threw on McGlashan and applied a little pressure before the last 13 minutes made for something of a horror show.
Tyson grabbed his second on 77 minutes, glancing home Buchanan’s corner at the near post, and made the match ball his own six minutes later, getting past Grimes to roar 25 yards into the box, home in on goal and despatch a shot for 3-0.
With the final whistle the only relief for the good number of away fans, Chesterfield rubbed salt in the wound before that, Smith’s delivery from the right dummied by Scott Boden and Curtis Weston simply had to take a touch and smack it home for the fourth.
It leaves Fleet seven points adrift of their opponents and with an immediate and redesignated target now of moving to within five points of Maidenhead instead this Tuesday – but that can only be done with a goal and a win.
EUFC: Gregory, Ekpiteta (Ugwu 78), King, Obileye (Grimes 16), Wilson (McGlashan 69), Blackman, Payne, Sutherland, Goddard, Mekki, Adeloye. Subs not used: Timlin, Holmes
CFC: Jalal, Cropper, Yarney, Evans, Hollis, Smith, Weston, Buchanan, Mandeville (Weir 69), Fondop (Tyson 57), Denton (Boden 86). Subs not used: Hutchinson, Fitzsimons
Attendance: 3,346 (126 EUFC)