Pompey produced a brave performance, but were beaten after extra-time to exit the EFL Cup at Coventry.
They were certainly not over-awed against their League One opponents and took the lead courtesy of a Curtis Main penalty.
But the hosts were much better after the break and goals from Ryan Haynes and Vladimir Gadzhev looked to have secured safe passage into the second round.
Kal Naismith levelled late on with a free-kick to ensure another 30 minutes, however, before Andy Rose finally won it for Coventry.
Paul Cook changed the entire side that started Saturday’s draw with Carlisle in the league.
He handed debuts to summer signings Adam Buxton, Tom Davies, Amine Linganzi and Main, while there was also a first appearance for teenage keeper Alex Bass.
Adam Barton was handed the captain’s armband against his former club, while Naismith featured in an unfamiliar left-back role.
But there was no sign of nerves from the visitors against their higher-ranked hosts in a half that was low on clear-cut chances.
Bass was able to steady any nerves by holding onto a couple of ambitious Coventry efforts from long-range.
Ben Tollitt scuffed a shot wide at the other end, while a Kyle Bennett cross was headed clear after the midfielder had done well to beat his man down the right.
But the Blues did break the deadlock on 19 minutes – and it was down to more good work from Bennett.
He tricked his way into the box and after being brought down by Marcus Tudgay, referee Andrew Madley pointed to the spot.
It was MAIN who stepped up to take the penalty and he confidently hammered it home, giving Reice Charles-Cook no chance.
But the keeper prevented the same player from having a chance to double the lead moments later, racing from his line to get to the ball first.
And it was Main who came close again on 22 minutes, forcing a decent stop from Charles-Cook after being teed-up by Bennett.
The hosts’ best chance of the first half arrived soon after, with Bass adjusting well to keep out Tudgay’s close-range header.
But Pompey were still proving to be an attacking threat themselves and Gareth Evans fizzed a shot narrowly over following good work from Tollitt and Adam May.
Half Time: Coventry 0 Pompey 1
Coventry looked sharper after the restart, but were still finding it difficult to breach the Blues back-line and test Bass.
Ben Stevenson decided it would be better to try his luck from long-range on 54 minutes and saw the ball fly wide.
Ruben Lameiras had a better chance moments later, firing over the bar following an almighty scramble in the box.
And the hosts finally made the pressure count by levelling the tie on the hour mark.
Davies could only head Lameiras’ cross as far as Haynes, who drilled a precise low shot past the grasp of Bass and into the bottom corner.
Pompey had looked ragged since the break, so Cook freshened things up by replacing Evans with Conor Chaplin on 64 minutes.
He immediately made an impact by getting free down the right, but his cut-back fell in between Bennett and Tollitt and the chance disappeared.
It was still Coventry looking more dangerous, however, and Lameiras skipped past Naismith, but could not beat Bass from an acute angle.
Kyel Reid then sent in a dangerous cross from the right that was inches too high for Jodi Jones, who was only able to head over.
And the hosts did go ahead on 82 minutes when Gadzhev collected Lameiras’ threaded pass and confidently tucked the ball home.
The lead did not last long, though, as NAISMITH was fouled by Stevenson just outside the box and picked himself up to curl a stunning free-kick into the top corner.
There might have even been a late winner before the full-time whistle when Chaplin and Noel Hunt exchanged passes, but the latter dragged his shot wide.
The duo combined again in stoppage-time and this time it was Chaplin who was off target with a looping header.
After 90 Minutes: Coventry 2 Pompey 2
Extra-time took a while to get going, but both sides had opportunities to score in the first period.
Bass made a couple of key saves, stopping Jones from sliding one in at the near post and also keeping out a drive from Lameiras.
Pompey’s best chance came when Tollitt released Hunt down the right and the striker squared for Bennett, who could not take it round Charles-Cook with just the keeper to beat.
But Coventry scored just moments into the second period, with Rose pouncing to tuck home the loose ball after Bass had pushed clear Haynes’ attempt.
They almost added another, only for Bass to produce a stunning stop to deny Lameiras from point-blank range.
And Pompey were unable to find a late moment of inspiration to take the tie to a penalty shoot-out.
Coventry (3-4-3): Charles-Cook; Willis (Finch 76), Ricketts (c), Harries; Rose, Gadzhev, Stevenson, Haynes; Thomas (Jones 46), Tudgay (Reid 68), Lameiras