In the end, Garath McCleary deprived Pompey of the extra-time opportunity to claim another Championship scalp in the Capital One Cup.
Yet Paul Cook’s men can be proud of another pulsating performance as they ran Reading close at Fratton Park tonight.
Once again the Blues were much-changed from their League Two side, on this occasion eight switches for the visit of the Royals.
However, as in their mighty 2-1 triumph over Derby County in the previous round, Cook’s shadow squad put in an admirable showing in front of a massive crowd of 18,190.
Pompey had even led the contest after 40 minutes through a stunning finish from an improbable angle courtesy of Conor Chaplin.
Another classy moment from the youngster greeted regularly with chants of ‘he’s one of our own’ by the Fratton faithful.
Nick Blackman cancelled that out in the 64th minute with an excellent run and finish after bursting in from the right-hand side.
It remained 1-1 until the 84th minute, with the Royals steadily stepping up the tempo, albeit failing to disturb Adam Webster and Matt Clarke too much at the heart of the Pompey defence.
However, with extra-time looming, the decisive moment was provided by substitute McCleary as he popped up unmarked at the far post to net the winner.
It marked a first defeat at any level for Cook since he took over as Blues boss in May – not that he could be downhearted.
A packed Fratton Park was treated to an exhilarating game of football, particularly in the first half, and his new regime continues to win many, many admirers in the city.
Although there were multiple alterations to the team which drew against Morecambe at the weekend, there was just the one change from the side which conquered Derby County in the previous round of the Capital One Cup.
That was Chaplin, coming in for Ben Davies, with Gareth Evans dropping in at right-back.
The call-up was reward for the 18-year-old, who made his first start of the campaign having notched the winner against the Rams after appearing from the bench that night.
Elsewhere, only Clarke, Evans and Kyle Bennett remained from the starting line-up for the 3-3 draw with the Shrimps.
That meant Paul Jones replacing Brian Murphy, Brandon Haunstrup coming in for the suspended Enda Stevens and Jayden Stockley taking the spot of Matt Tubbs as the lone striker.
Webster partnered Clarke at centre half, with the two defensive midfield spots – in place of Michael Doyle and Nigel Atangana – going to Ben Close and skipper Danny Hollands.
Completing the changes was Adam McGurk, who also netted in the last round, joining Chaplin and Bennett as the attacking midfield three.
However, top scorer and Saturday’s two-goal midfielder Gary Roberts was named on the bench just in case his services were required.
There was also a first squad appearance of the season for James Dunne, who took his place among the substitutes with his Pompey future still very much in doubt.
The hosts kicked the game off and on eight minutes Bennett twisted and turned to create space and flight a superb cross towards Stockley which Anton Ferdinand just managed to flick away.
Moments later, Evans drilled in a cross from the right but, unlike Saturday, Stockley’s diving header lacked accuracy and went wide.
The Blues were growing into the game and a period of sustained possession resulted in McGurk clipping a low cross in from the left which Ali Al-Habsi came out to gather.
At the other end, Simon Cox lifted a shot over the bar in Reading’s first meaningful attempt on goal.
Jones had to then come off his line to bravely block Blackman at the far post with an aerial challenge.
On 25 minutes, Chaplin produced a snap-shot from 25 yards which had Al-Habsi scrambling to his left to gather.
The hosts should have taken the lead minutes later when Hollands clipped a ball down the left and Bennett produced wonderful control and then sublime skill before crossing into the box.
There was Stockley with a right-foot volley from three yards out which somehow missed the target completely and flew out for a goal-kick.
Within seconds the Royals were at the other end with Hal Robson-Kanu outmuscling Webster and firing in a shot which was saved low to his right by Jones, who had rushed off his line.
The match was proving to be an entertaining affair and when Chris Gunter’s cross was clawed out by Jones, Cox lifted a follow-up attempt over the bar.
Yet in the 40th minute Pompey took the lead with a stunning finish from an acute angle by Chaplin.
Hollands started it off with a ball over the top and when Al-Habsi and Michael Hector dallied on the edge of the area, Chaplin nipped in to round the keeper and shoot home with his left-foot.
It remained 1-0 as the sides went in at the break with Fratton Park once again buzzing at the prospect of another upset.
On 49 minutes, McGurk linked up well with Hollands who threaded a pass through to Chaplin but his first-time left-foot shot curled narrowly wide.
Pompey were looking comfortable as the visitors attempted to find a way back into the match.
Danny Williams sent a shot over the bar – to the derison of the Fratton faithful.
Yet on 64 minutes the scores were level when Blackman cut in from the right – leaving Clarke for dead – and crashed a shot inside Jones’ near post.
It was an excellent finish from the ex-Sheffield United striker, who celebrated by putting a finger to his lips in the direction of fans in the South Stand who had earlier heckled him.
The encounter had calmed down compared to the first half but on 78 minutes Bennett did fire in a shot from long range which Al-Habsi dealt with.
Cook made his first substitution a minute later with Dunne coming on for McGurk and the returning midfielder got a generous reception.
Then in the 84th minute, Robson-Kanu charged down the left and fed Stephen Quinn, who teed up the unmarked McCleary at the far post to finish.
Pompey kept pushing – heartened by four minutes of time added on – but no equaliser was forthcoming as the visitors held out to progress.