Calvin Andrew’s winner earned Mansfield Town ‘derby day delight’ as The Stags inflicted a first defeat of the campaign on arch-rivals Chesterfield.
Andrew grabbed his first goal for The Stags shortly before half-time, when he rose highest to convert Ben Hutchinson’s superb corner.
Goalkeeper Alan Marriott was also a hero, thwarting The Spireites on numerous occasions, in order to keep his fifth clean-sheet of the season.
Chesterfield’s Gary Roberts was red carded for a blatant stamp on James Jennings in stoppage-time, as Mansfield recorded a memorable win.
The two teams meet again in the Second Round of the Johnstone’s Paint Trophy, in just 10 days time.
The Spireites had the first opportunity after just five minutes, when Jimmy Ryan’s powerful right-foot drive from 25 yards was superbly tipped round the post by Marriott.
Moments later, Marriott did superbly to claim a low left-sided cross by Ritchie Humphreys, which was intended for Eoin Doyle at the far-post.
The Stags created their first on the quarter-hour mark, but Jamie McGuire was unable to test Spireites stopper Tommy Lee with a 25-yard half-volley.
Chesterfield soon went close again as Doyle did well to retrieve an over-hit cross by Jay O’Shea and hit an angled strike, which was tipped over by a back-peddling Marriott.
Roberts also had a free-kick deflected over by The Stags’ defensive wall midway through the first period, as The Spireites began to enjoy a sustained spell of pressure.
Humphreys’ whistled a low left-wing ball into the six-yard box on 26 minutes, which somehow evaded Doyle, who was lurking dangerously at the far-post.
Humphreys, Doyle and Roberts all had chances within a frantic sixty-second spell, but Paul Cook’s side were still unable to make a break-through.
Doyle also headed wide from Drew Talbot’s ball, before The Spireites spurned a gilt-edge opportunity to take the lead on 33 minutes.
Roberts slipped a fine low pass through to an advancing Doyle, who lacked the composure to finish in a one-on-one with Marriott, as The Stags keeper made a smart save.
Mansfield responded almost instantaneously as, at the other end, Clucas whistled a low shot narrowly wide of the left-hand post.
On 38 minutes, however, the deadlock was finally broken, and it was the 2,000 travelling faithful from North Nottinghamshire, who had reason to celebrate.
Ben Hutchinson’s right-sided corner was met at the far-post by Andrew, whose powerful header flew beyond Tommy Lee and nestled beautifully in the net.
Now buoying with confidence, The Stags nearly doubled their advantage just a few moments later, as Hutchinson’s stab-shot inside the area, cannoned back off the post.
By now, the match had broken into a ferocious encounter, with the pendulum constantly swinging to-and-forth.
Chesterfield attempted to use width at every available opportunity, in an attempt to break down the resolute visitors, and almost equalised on the brink of added-time.
Following some good play on the left flank, Roberts found Sam Morsy with a deep cross into the six-yard box, whose header ricocheted off the upright.
Tafazolli subsequently cleared the danger, which ensured that The Stags held the advantage going in to the half-time interval.
Chesterfield began brightly after the re-start as they sought to quickly find an equaliser and maintain their unbeaten start to the campaign.
Humphreys almost found a blue shirt with another inviting low cross through the six-yard box, before Roberts blazed over with a 25-yard free-kick.
The Spireites made a double change on 53 minutes, when Armand Gnanduillet and Gary McSheffrey replaced Tendayi Darikwa and O’Shea respectively.
However, it was The Stags who enjoyed the next chance as Ryan Tafazolli evaded the offside trap, but headed wide after James Jennings’ intelligent free-kick.
Chesterfield soon regained the momentum, and Marriott was forced to keep out Roberts’ low strike, before Morsy was cautioned for diving.
The Spireites were starting to pen Mansfield back and went close again prior to the hour-mark.
Gnanduillet tried his luck with an ambitious drive from distance, which Marriott could only parry, but Humphreys horribly blazed over on the follow-up.
Mansfield made a tactical substitution on 62 minutes, when Hutchinson was withdrawn in favour of Lindon Meikle, who went to a wide-right position.
By the midway point in the second half, much of the home crowd had become anxious and frustrated at their teams inability to make a break-through.
Nevertheless, The Spireites were still creating chances and after McSheffrey fired a free-kick straight at The Stags’ wall; Doyle had a separate effort saved.
As the match approached its pulsating finale, Chesterfield continued to pressurise their counterparts, and threw everything forward.
On 77 minutes, Morsy and Doyle both turned away in anguish as they had separate attempts kept out by Marriott, who was having a superb match.
The Stags’ custodian made another fantastic save moments later when he had to quickly re-adjust his position in order to save Ryan’s long-range strike.
In an act of utter desperation, Chesterfield made their final substitution with just a few minutes left to play, as Drew Talbot was replaced by Jamie Devitt.
However, despite The Spireites continuing to enjoy more possession, it was Mansfield that looked the more likely to score, on the counter-attack.
Substitute Matt Rhead, who brilliantly held the ball up at every opportunity after his introduction with 10 minutes to go, fired straight at Lee, after Meikle’s low through-ball.
Lee’s save could have proved valuable as, incredibly, there were six minutes of added time.
But whilst the travelling Stags fans bit their nails and counted down every single second, The Spireites were forced to endure more frustration.
In the third minute of stoppage-time, Roberts was rightly dismissed when he appeared to stamp on a grounded Jennings.
After nearly 97 minutes of intense, gripping and captivating drama, the final whistle finally sounded to euphoric roars of celebration from The Stags’ fans.
The victory will undoubtedly go down in Stags folklore, whilst Chesterfield fans, by stark contrast, will no doubt want to forget this derby day defeat.