Pompey crashed out of the Emirates FA Cup at the first hurdle with a home defeat to fellow League Two outfit Wycombe.
They were poor before the break and deservedly trailed to Paris Cowan-Hall’s close-range finish.
There was a marked improvement after it, though, and Gareth Evans drew the hosts level following the restart.
The tie appeared to be heading for a replay, only for Adebayo Akinfenwa to strike late on and book Wanderers a place in Monday’s second round draw.
Paul Cook made five changes from the side that won at Cambridge in the league the previous week.
Noel Hunt was handed a first start in attack, while Adam Buxton, Ben Close, Danny Rose and Milan Lalkovic all returned.
Conor Chaplin, Carl Baker and Kyle Bennett dropped to the bench and Pompey were missing the suspended duo of Michael Doyle and Amine Linganzi.
The hosts started brightly on a crisp afternoon on the south coast and won a number of corners that caused the Chairboys problems.
But Wycombe soon started to take control and almost forged ahead when Matt Bloomfield drilled in a low shot that cannoned back off the post.
They went close again moments later, with David Forde just about getting a leg to Cowan-Hall’s effort and diverting the ball wide.
And Wanderers were unable to make it third time lucky when Dominic Gape struck a long-range shot past the post.
But it seemed like only a matter of time before the visitors breached the Blues’ goal and the opener did arrive on 27 minutes.
There was a slight touch of fortune about it, however, with Forde punching clear Michael Harriman’s free-kick, only for the ball to ricochet off the back of Christian Burgess.
Former Pompey youth player Cowan-Hall was in the right place to follow up and head home from just a few yards out.
That failed to spark an upturn in the attacking fortunes of the Blues, though, with Wycombe still looking the more threatening.
There were half-chances for Cowan-Hall and Luke O’Nien, but their best chance of doubling the lead came in stoppage-time.
A corner found Akinfenwa at the far post, only for the imposing striker to head wide from close range.
Wycombe Wanderers 1
Pompey had failed to trouble Jamal Blackman before the break, but the keeper was picking the ball out of his net just a couple of minutes after the restart.
Enda Stevens whipped in a teasing cross from the left and EVANS found space in the box to deftly tuck home.
They might have scored another moments later, but Blackman tore from his line to beat Gary Roberts to Close’s threaded pass.
Cook made a double switch just past the hour mark, with Lalkovic and Buxton withdrawn for Bennett and Baker.
But it was Wycombe who almost retook the lead 65 minutes, with Akinfenwa seeing one shot blocked and then the second saved by Forde.
Baker went close himself moments later, however, with a fierce 30-yard strike that was brilliantly palmed over by Blackman.
Cook then made a final throw of the dice on 75 minutes, with the in-form Chaplin replacing Hunt up front.
But the Blues were indebted to Forde for keeping them on a level pegging with two key saves soon after.
The first saw him just about get something to a shot from Myles Weston that took a wicked deflection to divert it off course.
Then, for the second, he dived backwards to palm over Akinfenwa’s cleanly-struck dipper from outside the box.
Both sides appeared keen to avoid a replay, showing plenty of attacking intent as the seconds ticked down.
But it was the hardy band of travelling supporters celebrating late on when Akinfenwa converted Garry Thompson’s cross.
There was hope of another leveller when the fourth official displayed an additional six minutes to be played.
The Chairboys held on to their slender lead, however, to ensure that cup magic was in short supply for Pompey.
Pompey (4-2-3-1): Forde; Buxton (Baker 64), Burgess, Clarke, Stevens; Close, Rose; Evans, Roberts (c), Lalkovic (Bennett 64); Hunt (Chaplin 75)
Goals: Evans 47
Subs not used: O’Brien, T.Davies, Naismith, Smith
Wycombe (4-3-3): Blackman; Harriman, Stewart, Pierre, Jacobson; O’Nien, Gape, Bloomfield; Hayes (c) (Thompson 77), Akinfenwa (Bean 89), Cowan-Hall (Weston 72)
Goals: Cowan-Hall 27, Akinfenwa 84
Subs not used: Brown, Jombati, De Havilland, Kashket
Referee: Gavin Ward
Attendance: 8,130 (510 away fans)