Aramand Gnanduillet headed a dramatic late winner to give the Spireites a 2-1 win at home to Southend, just at it looked as though they would have to settle for a point.
Gnanduillet, on as a substitute, found the net in the fifth minute of stoppage time to spark scenes of joy at the Proact as the Frenchman celebrated.
Gary Roberts had put Chesterfield in front just before the hour-mark with a fine free-kick before Freddie Eastwood equalised nine minutes later.
With Roberts given the go-ahead to continue after doubts over his fitness, Paul Cook made just one change to his starting line-up with the fit-again Liam Cooper replacing Ryan Edwards in central defence.
Conor Clifford, who had a spell on trial with the Spireites in pre-season, was named in the Southend side.
Chesterfield started brightly with Drew Talbot sending over a searching cross which was gathered by keeper Dan Bentley at the second attempt as Marc Richards waited to pounce.
Richards then threatened after racing on to a ball from Roberts, side-stepping Bentley before firing wide from an acute angle under pressure from Adam Thompson.
Southend’s first effort came from John White who put a low shot straight at Tommy Lee. Anthony Straker then saw his shot deflected off-target.
Chesterfield countered with Ritchie Humphreys heading over from Nathan Smith’s cross and Roberts, who was off-balance, volleying off-target.
Bentley pulled off a superb save to turn over a 30-yard effort from Jay O’Shea which looked destined from the top left-hand corner of his net.
At the other end, Cooper made an important challenge to dispossess Eastwood in the area and White had a shot blocked.
After a shot from Talbot was comfortably saved, Clifford had a shot deflected off-target and Corr missed the target with a free header.
Roberts (59) opened the scoring, finding the top right-hand corner of Bentley’s net with a superb free-kick.
Eoin Doyle then joined the action, replacing Richards, to join Tendayi Darikwa who had taken over from Humphreys earlier in the half.
The Shrimpers equalised in the 68th minute when the ball fell kindly to Eastwood in a central position on the edge of the area and the striker beat Lee with an impressive finish.
Roberts won a free-kick on the edge of the ‘D’ and must have fancied his chances of finding the net for a second time but his low strike was well saved by Bentley, down low to his right.
After Cook made a third substitution, sending Gnanduillet on in place of O’Shea.
The impressive Bentley dealt comfortably with a Jimmy Ryan free-kick and then saw Gnanduillet shoot straight at him.
Southend’s Luke Prosser threatened in stoppage time, seeing his first effort blocked and his follow-up turned wide by Lee.
Sam Morsy then saw his shot turned wide by Bentley and from the resulting corner, taken by Roberts, Gnanduillet scored with a firm header to delight the Spireites fans.
Chesterfield: Lee; Talbot (c), Hird, Cooper, Smith; Ryan, Morsy, O'Shea (Gnanduillet 77'), Humphreys (Darikwa 56'), Roberts; Richards (Doyle 64').
Subs not used: Chapman, Edwards, Togwell, Devitt.
Southend United: Bentley, White (c), Coker, Prosser, Eastwood (Timlin 83'), Corr (Cowan 78'), Straker, Atkinson, Clifford (Hurst 60'), Leonard, Thompson.
Subs not used: Smith, Reid, Payne, Banton.
Goals: Chesterfield (Roberts 59', Gnanduillet 90+4') 2 - 1 Southend United (Eastwood 68').
Attendance: Chesterfield - 5579 Southend - 369