A 95th-minute goal from Andrew Dallas saw Chesterfield complete a second-half comeback to beat Eastleigh 3-2 at the Technique Stadium.
The Spitfires had taken a two goal lead into the break thanks to goals from former Chesterfield duo Kairo Mitchell and Charlie Carter, before Ryan Colclough drew the game level with a brace.
Dallas secured the win for the Spireites, and their place in the playoffs, with a inch-perfect shot from the edge of the box in the final minute of injury time.
After a bright and fast-paced start, Eastleigh took the lead on 10 minutes, sending the Technique Stadium into hushed silence.
A corner from Michael Kelly bounced around in the box before Mitchell slammed the ball through a sea of players and into the net.
Rutherford charged down the right before cutting inside, shrugging off two tackles in the process before sending a shot into the hands of Ross Fitzsimonds.
Vincent Harper was introduced on 19 minutes as Lee Bradbury was forced into an early change when Alfie Lloyd went down injured following a collision with Fitzsimonds.
After an off-the-ball incident, which saw Mitchell and Fitzsimonds receive yellow cards, the hosts came close to scoring a equaliser through Ryan Colclough, but he was denied by a deft touch from Joe McDonnell.
Clolcough was heavily involved once more moments later, he got in behind Oscar Rutherford before teeing up Darren Oldaker, who saw his effort cleared away by George Langston.
For all of Chesterfield’s pressure, they couldn’t find an equaliser and the Spitfires made them pay.
A sharp move from back to front saw the eventually at Danny Whitehall’s feet, his effort was rebounded into the path of Carter, who calmly dispatched his 11th goal of the season to double Eastleigh’s lead on 33 minutes.
The Chesterfield fans were up on their feet on 62 minutes thinking Joe Quigley’s header way about to half the deficit, but McDonnell produced a fantastic save to turn the ball onto the post, before the linesman raised his flag.
Having been introduced on 59 minutes Gerry McDonagh had to be withdrawn 11 minutes later after he picked up an injury. Nigel Atangana was brought on in his place to provide extra defensive reinforcement as Eastleigh looked to close out the game.
But, on 72 minutes, Colclough headed home a Liam Mandeville cross to cut the Spitfires lead in half, re-energising the home side and their supporters.
Andrew Dallas’ low-driven shot flashed just past the post as Chesterfield with 10 minuets left as pushed hard for an equaliser.
The equaliser did eventually come when Colclough converted a Jeff King cross from the right to score his second of the afternoon.
With five minutes of additional time added at the end of the second half there was enough time for the hosts to score a winner.
Dallas cut in from the right before bending a perfectly placed shot into the bottom corner, out of McDonnell’s reach.
Chesterfield: Fitzsimonds, King, Palmer, Grimes (C), Maguire, Jones, Banks, Mandeville, Oldaker, Colclough, Quigley
Subs: Horton, Uchegbulam, Asante, Dallas, McCallum
Eastleigh FC: McDonnell, Rutherford, Maghoma, Langston, Kelly, Cisse (C), McKiernan, Carter, Lloyd, Whitehall, Mitchell
Subs: Camp, Martin, Atangana, Harper, McDonagh
Attendance: 6,733 (74 away fans)
Match report by George Rees-Julian