In a frenzied opening at a helter-skelter pace two goals came in the first nine minutes - and the goalmouth action continued right up to the last minute when Mansfield striker Michael Boulding was denied a last-gasp equaliser by keeper Barry Roach.
Then in stoppage time, with the Stags pressing for an equaliser, Jack Lester broke clear to secure victory, rounding the keeper and rolling into an empty net.
Chesterfield had got off to the best possible start with a goal after 130 seconds, Gregor Robertson's in-swinging corner somehow squirming through the grasp of the diving former Spireite keeper Carl Muggleton, who saw the ball late through a crowded penalty area.
Two minutes later the Stags thought they had levelled, but John McAliskey's finish from a Matt Hamshaw cross was ruled out for offside.
Then Stephen Dawson's thumping 25-yard drive from a partially cleared corner was tipped around the post by the diving Roach.
But Dawson made no mistake from the resulting corner, crashing an unstoppable left-footed volley past the despairing Roach from 22 yards to level after just nine minutes.
Stags keeper Muggleton redeemed himself in the 18th minute, bravely racing out to save at the feet of Lester, but was then fortunate when Derek Niven created a chance for Lester to head narrowly wide.
Chances continued to come thick and fast for the rest of the first half. For the Stags Boulding cut past two defenders, but just failed to pick out the incoming Sean McAllister when he might have shot himself, and then the striker wriggled clear only to be blocked by the on-rushing keeper.
Chesterfield's Jamie Lowry shot wide from 20 yards and then Kevin Gray headed narrowly past the far post from a deep free-kick with just the keeper to beat.
In an amazing scramble on half-time the Stags somehow survived a glut of Chesterfield chances as the ball pinged across the penalty area. A fine diving block by Martin McIntosh thwarted Lowry, Fletcher headed against the bar, and Lester's pile-driver was blocked.
But a Chesterfield goal seemed inevitable and it arrived in the final seconds of the half. Keeper Muggleton failed to reach Peter Leven's skidded low shot, deflected by Fletcher, and when it rebounded off the post Lowry thumped in from close range.
A minute into the second half Leven's dipping 25-yard drive caught out the hesitant Muggleton again, but this time the ball bounced to safety off the bar.
Almost immediately Dawson's clever pass released Boulding at the other end, but with just the keeper to beat the striker's low shot struck the foot of Roach.
Then the unmarked McIntosh headed Hamshaw's free-kick wide as the home side pressed for an equaliser.
Roach was lucky to avoid a red card after racing out of his area to foul Boulding as the striker raced clear. The injustice of his yellow card for a professional foul was immediately shown when he dived full length to punch away McIntosh's resulting free-kick.
It was highlighted again 16 minutes from time when Mansfield captain Jake Buxton was dismissed for his second yellow card.