Revamped Pompey were undone in extra-time as their EFL Cup distraction ended at the Ricoh Arena.
With Paul Cook’s priority undeniably winning promotion, he ripped up his team to make 11 changes against Coventry City last night.
It was a starting line-up which included two teenagers, one of which making his first-team debut, and four players handed their bows for the Blues.
Nonetheless, Cook’s understudies produced an encouraging display full of heart and endeavour before they were eventually seen off by their League One hosts during extra-time.
Kyle Bennett earned the penalty for Curtis Main to give Pompey a 19th-minute lead – an advantage they retained for the remainder of the first-half.
However, the half-time introduction of forward Jodi Jones transformed the Sky Blues’ performance as they dominated after the break.
Ryan Haynes levelled on the hour mark before Vladimir Gadzhev struck on 82 minutes to seemingly clinch victory.
But Kal Naismith’s stunning free-kick levelled the match and sent it into extra-time.
It was Tony Mowbray’s side, though, who took the win – Andy Rose’s 106th-minute finish settling the occasion.
Yet much-changed Pompey, prompted by impressive debutant Amine Linganzi in midfield, can be well satisfied with their performance.
With no restriction on team changes, Cook overhauled the line-up which started against Carlisle at the weekend.
There were debuts for Alex Bass, Tom Davies, Adam Buxton, Linganzi and Main as Pompey’s squad was rotated.
Naismith continued his return from the cold by being named at left-back, while the 18-year-old Adam May made his second start for the club.
Gareth Evans was back in the team having recovered from the ankle and knee ligament injuries collected in the play-off semi-final defeat to Plymouth.
Bennett, Ben Tollitt and Adam Barton completed the starting line-up, while recent recruit Liam O’Brien was among the seven substitutes.
In contrast, Mowbray made three alterations to the side which suffered a late loss against Swindon on Saturday.
Operating with a 3-4-3 system, Ruben Lameiras, Ben Stevenson and Marcus Tudgay were called into the side in place of Jones, Dion Kelly-Evans and Marvin Sordell.
When the match got under way, it was the Sky Blues who won the first corner on three minutes as Barton read a ball down the left channel and put it out.
After several attempts at getting the set-piece high enough into the box to cause problems, Barton crashed the ball clear and any danger was averted.
On nine minutes, Haynes was too comfortable breaking down the left flank yet his cross was too close to Bass, who gathered.
The youngster was again called into action moments later when he dived forwards to comfortably take Haynes’ drive from 30 yards.
Bennett provided an eye-catching moment when he dispossessed Stevenson and then outfoxed him with skill to create space for a dangerous cross which was cleared.
The visitors were growing in stature and on 17 minutes Tollitt drove in a ball from the right which Main laid to the path of May, whose first-time shot was deflected for a corner.
Pompey did, however, break the deadlock on 19 minutes through excellent Bennett play.
The winger wriggled his way into the box before falling to the ground under a challenge from Tudgay, with a penalty awarded.
Furious Coventry players confronted Bennett claiming it was a dive – with Lameiras booked for his reaction – and Main stepped up to net with a powerful right-foot finish.
Moments later, Bennett’s cross-cum-shot was diverted goalwards by Main, only for Reice Charles-Cook to change direction and take the ball high.
At the other end, Bass was put under pressure when he failed to hold the flying Tudgay’s header but Pompey managed to clear the danger.
Bennett was presented with a glimpse of goal on 34 minutes when May’s pass put him through down the left channel, yet he elected to square a pass and it was intercepted.
Evans then enjoyed his most meaningful moment so far with a rasping right-foot drive from long range which narrowly cleared the crossbar.
Still losing at half-time, Coventry introduced Jones for George Thomas at the break as they attempted to find a way back into the match.
The hosts began to enjoy their best period of the game, putting the Blues under a steady stream of pressure after the break.
On 54 minutes, Stevenson flashed a left-foot shot wide of the far post as they continued to press.
Next Lameiras blasted over from close range with the visitors struggling to keep the Sky Blues at bay.
They finally levelled on 60 minutes when Lameiras crossed from the right and Davies’ header fell to Haynes.
The striker calmly lashed the ball past Bass on the angle – and Coventry had made their second-half pressure tell.
Cook made his first substitution on 64 minutes with Conor Chaplin replacing Evans, allowing Bennett to switch to the left and Main to drop into the hole.
Chaplin’s first contribution was to roll the ball invitingly across the box, only for Bennett and Tollitt to get in each other’s way and the chance petered out.
Yet Coventry continued to dominate and the impressive Jones was a whisker away from heading home Kyel Reid’s cross after the substitute had left Barton for dead.
In the 82nd minute, Coventry had their lead when Lameiras put through Gadzhev and the midfielder did the rest.
Within three minutes it was 2-2, Naismith winning a free-kick before taking it himself and curling home a brilliant left-foot finish from 25 yards. During four minutes of time added on, substitute Noel Hunt sent a shot wide, while a looping Chaplin header was narrowly off target.
The first half of extra-time saw Bass save low down from Jones, while Bennett allowed Charles-Cook to close him down by dallying after Hunt squared a pass.
However, at the start of the second period Rose restored Coventry’s lead.
Haynes’ curling shot from the left was parried by Bass and Rose was there at the far post to turn the ball home via a deflection off Barton.
That finally settled the fixture as Coventry progressed and the Blues found themselves with one less competition to distract them.