It took two minutes. Ecstasy to agony during an exhausting season for players and supporters alike.
With the scoreline locked at 2-2, Brett Pitman bore down on the Fratton End, left with just the keeper to beat.
Substitute Viv Solomon-Otabor was located to his left, albeit in an offside position – Pompey’s skipper unselfishly elected to pass.
The Birmingham loanee netted in that 73rd minute, yet the linesman’s inevitable flag intruded upon celebrations.
Within 120 seconds, Peterborough were rejoicing after grabbing the goal which had earned them a 3-2 victory.
Ivan Toney squeezed home a shot into the far corner of the net following more poor Blues defending. It was over.
A second for the match from the handful of a striker, with Kenny Jackett’s side barely able to muster a meaningful attempt on goal from thereon in.
Darren Ferguson’s side, like the hosts, required a win. Their play-off aspirations depended on it and in that microcosm of action the occasion was settled in their favour.
Likewise, defeat for Sunderland, in stoppage-time at Fleetwood, ensured Luton and Barnsley claimed League One’s automatic promotion spots with a match to spare.
Pompey’s players were applauded off the pitch by the appreciative Fratton faithful, rightly so considering the remarkable promotion push since defeat at Charlton.
The night may have shattered aspirations of finishing in the top two but the home support recognised the immense effort their side had applied during the campaign’s marathon.
The Posh had even taken a 2-0 lead after 27 minutes, despite a stirring start from Jackett’s man.
Sadly, their inability to keep clean sheets during the second half of the campaign was once again apparent, found wanting defensively against a side they may now meet in the play-offs.
Disappointingly, the visitors had netted with their first attack, Lee Tomlin scoring on 13 minutes.
Then Toney was criminally unmarked as he powered home a header 14 minutes later.
Jackett’s men rallied – this side so full of heart and resilience – through Ben Close and then, on 59 minutes, Christian Burgess.
Pompey had the impetus, they possessed the momentum, then Pitman and Solomon-Otabor launched a two-pronged attack with 17 minutes remaining.
The pair will both be ruing individual decisions in that crucial moment, Solomon-Otabor for straying offside and Pitman for not recognising the danger of a pass.
And, within two minutes, Pompey’s automatic promotion hopes were over.
Now on to the play-offs, with Saturday's final match against Accrington to settle the forthcoming semi-final opposition.
For the visit of Peterborough, former Posh loanee Omar Bogle returned to Pompey’s squad following knee and ankle injuries.
He bolstered an attacking bench which included Anton Walkes as the sole defender in a match the Blues had to win to maintain their promotion ambition.
As for the starting line-up, that was unchanged, with James Vaughan handed his full debut at Fratton Park following a Sunderland outing which impressed the manager.
Ronan Curtis also retained his place as he strives to rediscover the form which saw him shine during the opening half of the campaign.
That meant Oli Hawkins and Gareth Evans remaining on the bench, although both endured disappointing entrances when thrown into the action at the Stadium of Light.
The only alteration to that 18-man squad on duty for Saturday’s 1-1 draw against the Black Cats was Bogle replacing Brandon Haunstrup among the substitutes.
When the match got under way, Pitman was given a sniff of goal on three minutes.
Clever play by Curtis down the left freed the overlapping Lee Brown and his cross was met by the skipper, getting ahead of his marker but nicking it well wide of the far post.
The Blues had started in dominant fashion and, when Brown put a cross in from the left, Vaughan cleverly headed it back and Curtis’ shot struck team-mate Jamal Lowe.
Then another Brown delivery fizzed across the face of goal, yet nobody could apply the crucial touch.
However, in their first attack, Peterborough took the lead on 13 minutes.
Marcus Maddison popped up down the right and slid the ball back for Tomlin to rifle a first-time shot into the far corner of the net.
Moments later, Jason Naismith shrugged off Curtis down the right and pulled it back, with Toney’s connection taking a slight deflection and comfortably finding Craig MacGillivray.
At the other end, on 18 minutes, the impressive Lowe crossed from the right and Ben White managed to get ahead of Vaughan to block his attempted shot.
The visitors increased their lead on 27 minutes through Toney.
Maddison aimed a corner from the left towards the far post and the unmarked striker galloped in to power a header past the helpless MacGillivray.
Tomlin collected the first booking of the game on 30 minutes after he was finally punished for time wasting.
There was an attempt from outside the box by Tom Naylor – having pounced on Pitman’s chested path – but he lashed it well over the bar.
Joe Ward was the next Posh player to receive a yellow card, bundling over Nathan Thompson after the defender had got the better of him.
It was 2-1 on 37 minutes, with Close reducing the deficit.
Curtis’ cross from the left was miskicked by Pitman, yet fell kindly to Close, whose right-footed shot clipped off the flying Josh Knight and looped over a helpless Aaron Chapman.
It reinvigorated Fratton Park and suddenly the Blues had themselves a crucial lifeline.
Moments later, the hosts had appeals for a penalty waved away after Thompson went down while attempting to retrieve Pitman’s clever dink.
Entering three minutes of time added on, Pitman slid Curtis through and the Irishman twisted his way towards goal, only to fire a left-footed shot straight at the keeper,
Then the Blues bloke down the middle, with Lowe feeding Curtis but his shot was saved by the feet of Chapman.
It was 2-1 at half-time and Jackett made a change, with Hawkins replacing Vaughan.
The second period started slowly, although Pompey did win a corner down the right on 53 minutes when Curtis’ free-kick was deflected.
The Irishman wasn’t on the pitch for the set-piece after he was replaced by Solomon-Otabor.
Pompey were stepping up the pressure and when Pitman crossed from the left, firstly Close’s shot was blocked before Lowe’s attempt from the angle was repelled.
Then, on 59 minutes, it was all-square through the unlikely Burgess.
Brown’s delivery from the left was nudged inside by Hawkins and Burgess took a touch before drilling a left-footed shot into the net.
The Blues had fought back from two goals down – now they searched for the winner.
Solomon-Otabor then raced through the middle with Pitman to his right and just one defender to beat, yet the substitute was caught in two minds and the ball was cleared.
Close went on to crash a dipping right-footed half-volley just over the bar from outside the penalty area.
It as captivating fare and when Maddison fired in a free-kick, MacGillivray couldn’t hold and Burgess completed the clearance.
Solomon-Otabor was looking lively and cut inside Maddison to unleash a shot which whistled just past the post.
On 72 minutes, Ryan Tafazolli sent in a thumping header from Maddison’s free-kick, which struck the bar and bounced clear, much to home fans’ relief.
Pompey got the ball into Peterborough’s net for a third time through Solomon-Otabor but he was in an offside position, fed by Pitman, who himself could have gone it alone.
Within two minutes the Posh had regained their lead through Toney’s second of the game, the forward drilling it into the far corner after breaking into the box.
Pompey were broken, they pushed forward but barely could create another opportunity.
It was defeat – and now the play-offs provide the passageway to the Championship.