From an offside position, Nathan Thompson handled during teeing up Matt Clarke for a stoppage-time winner.
It was Pompey’s day.
Consecutive win number seven claimed at the death amid the most melodramatic of circumstances.
Certainly the Blues’ promotion charge has lacked such theatrics during the season’s duration. Well, no more.
As the final whistle sounded three minutes later, Thompson and Christian Burgess collapsed to the floor, before lying supine on their backs.
It had been an exhausting effort from the valiant Blues in a Burton encounter they would have gratefully grasped a point considering how it unfolded.
Pompey had to defend manfully throughout against a Nigel Clough side which this month had already taken points off Sunderland and defeated Barnsley. It was easy to see why.
Some would claim the visitors deserved nothing, although their resilience, aptitude and heart unquestionably warranted reward. Perhaps a point – yet it turned out to be all three.
They returned south with a hard-fought 2-1 triumph which had those present of Brewers allegiance spitting expletives.
Referee Craig Hicks, his near-side assistant and, of course, Thompson were the dastardly villains and subjects of their fury following a flagrant heist.
Nonetheless, the countdown now shows four victories required to reach the Championship.
Unjust it may have been, but the gutsy Blues defended as a team, demonstrating impressive desire which should be applauded.
In fairness, Pompey had even occupied a winning position at half-time, albeit entirely against the run of play in an often-testing first period.
Ben Close, who days earlier had signed a new Fratton Park deal, cracked home a lovely left-footed shot on 31 minutes to put then in pole position, yet definitely not in charge.
Then, two minutes into the second half, Liam Boyce headed home Colin Daniel’s cross and the match was on level terms.
Buoyed by the substitute entrance of Bryn Morris, Omar Bogle and finally Ronan Curtis, the Blues did improve from the hour mark.
Then, during four minutes of time added on, Curtis crossed from the left, Bogle flicked it off the top of his head – and Thompson and Clarke did the rest.
Jackett had made one change to the team which defeated Rochdale 4-1 last weekend.
It was Curtis who was replaced by Gareth Evans on the left of the attacking three as the Irishman’s fitful form since his finger injury continues.
Evans made a scoring entry from the bench in that victory over the Dale, having replaced Curtis in a role which is now growing in familiarity.
As a consequence, Jackett restored the long-serving midfielder to his starting XI for the Pirelli Stadium encounter.
Elsewhere, fit-again Viv Solomon-Otabor was among the substitutes following a successful reserve-team comeback at AFC Bournemouth on Tuesday.
A 65-minute outing was enough to convince the Blues that he is now over the calf problem which condemned him to a month on the sidelines.
The Birmingham loanee replaced Louis Dennis on the bench, while once again there was no room in the 18-man squad for James Vaughan.
Meanwhile, Andy Cannon travelled as stand-by as he seeks a first-team return following three months out with a quad injury.
When the match got under way, Pompey won an early corner down the right, which was delivered left-footed by Lee Brown.
Matt Clarke flicked on at the near post, but the ball sailed over the bar without troubling keeper Stephen Bywater.
At the other end, a promising home move down the right saw Lucas Akins whip in a dangerous cross, but a sprawling Nathan Thompson had been fouled and the free-kick awarded.
On eight minutes, Evans’ corner from the left couldn’t quite find the head of the charging Tom Naylor at the far post, fractionally eluding the former Brewers midfielder.
Liam Boyce should then really have done better when John Brayford flung in a cross from the right towards Marcus Harness which fell invitingly into his path charging in.
However, his half-volley lacked a good connection and the ball ran harmlessly through to Craig MacGillivray in the visiting net.
The pressure was building and Jamie Allen fired a right-footed shot narrowly wide from outside the box after advancing centrally.
A Blues counter-attack was launched on 26 minutes when Oli Hawkins’ slide tackle dispossessed Kyle McFadzean and Brett Pitman put away Close.
The midfielder’s right-wing cross was gathered by Bywater fractionally before Evans arrived, the Pompey man having to hurdle the keeper in the process.
The deadline was broken in the Blues’ favour on 31 minutes through Close.
Thompson retrieved an over-hit cross delivered from the left and smartly slid a pass inside to Close, who struck a wonderful first-time right-footed shot into the far corner.
Jackett’s men had been forced to defend for spells of the first half, yet now had the lead at the Pirelli Stadium.
Bywater, recalled following a groin injury to regular keeper Bradley Collins, was looking uncertain and, at one stage, let the ball bounce over his head, to move clear on goal, only for the offside flag to rescue him.
Close received the first booking of the afternoon when, on 43 minutes, he slid into a poor challenge on Stephen Quinn.
Moments later, Hawkins galloped down the right and pulled the ball back into the path of Pitman, who rattled a first-time right-footed shot over the bar.
The visitors held the advantage until the break – yet two minutes after the restart the scoreline was level.
Left-back Daniel delivered an excellent cross from the left and there was Boyce with a towering far-post header to make it 1-1.
The Brewers had been rewarded for their persistence and moments later Lucas Akins fired in a powerful right-footed shot straight at MacGillivray.
On 57 minutes, Hawkins won a free-kick down the left and Evans’ delivery was headed goalwards by Burgess, only for Bywater to superbly tip over.
At the other end, MacGillivray pushed Quinn’s shot around the post after Brown had lost possession down the left.
Pompey made a double substitution on 61 minutes when Pitman and Hawkins were replaced by Bryn Morris and Omar Bogle.
The visitors continued to find themselves under pressure, though, as the Brewers maintained their attacking threat.
On 71 minutes, Evans put Bogle in down the left, yet the striker’s angled shot lacked power and was comfortably gathered by Bywater at his near post.
Substitute Morris had a glorious opportunity to score on 76 minutes when Brown pulled the ball back from the left and the midfielder’s first-time left-footed attempted curled well wide.
Curtis then entered the fray, in place of Evans, for the Blues’ third and final substitution.
And the Irishman was fully involved in that dramatic finale which ensures Pompey are four wins away for Championship football once more.