Conor Shaughnessy headed home in stoppage-time as Pompey once again battled from behind to beat Wycombe and stay top of the League One table.
The visitors had stunned Fratton Park by taking the lead through Josh Scowen in a first half that was otherwise controlled by the hosts.
They had not turned that into meaningful openings, but that changed after the break and Colby Bishop eventually levelled.
And the ground erupted right at the death when Shaughnessy rose highest in the box to score his first Blues goal.
John Mousinho made one enforced change from the side that won on the road at Wigan on Saturday.
Marlon Pack injured his ankle in the challenge that saw Charlie Wyke sent off, so Tino Anjorin was handed a full debut and Joe Morrell took the captain’s armband.
The hosts looked to make a fast start and soon began to apply pressure, but were struggling to get through and test Max Stryjek.
Garath McCleary flashed a shot wide at the other end, but it was still against the run of play when the Chairboys broke the deadlock.
Luke Leahy swung in a corner – their only one of the first half – and Scowen got between a couple of players to convert it from close range.
Pompey were seeing plenty of the ball as they tried to hit back, but their attacks were too often fizzling out in the final third.
A dangerous delivery from Abu Kamara was nodded behind by Leahy before it could reach Paddy Lane at the back post.
There were also a series of corners from Jack Sparkes that Wycombe did well to get away from danger.
And when Stryjek did not get a clean punch on one of those centres, the ball would not quite land right for Alex Robertson to get a shot away.
Half Time: Pompey 0 Wycombe 1
The hosts made a fast start to the second half and when a Joe Rafferty cross drifted towards goal, it had to be turned over by Stryjek.
Sparkes then swung in another excellent corner, but again Wanderers were able to get the ball to safety.
And a good chance was wasted when Anjorin received a pass from Rafferty in space and fired over the bar.
Mousinho freshened things up with a substitution on 56 minutes, as Anjorin made way for Christian Saydee.
Pompey were inches away from levelling the contest moments later, but a stretching Kamara could only turn the ball wide after meeting Lane’s drilled delivery across the face of goal.
And they finally made their pressure count when Kamara raced onto a Sparkes throw and cut the ball back for BISHOP to poke home.
But the hosts received a blow when Robertson was booked for a high boot, ruling him out of Saturday’s clash with Port Vale.
The Blues were still winning plenty of corners and one from the Australian loanee was nodded narrowly past his own post by Richard Keogh.
Poole was then shown his fifth yellow card of the season for a foul on Scowen, also ruling the defender out against the Valiants.
With the home side still in search of a winner, Gavin Whyte was brought on and Lane given a chance to rest up.
The chances had started to dry up, but there was an opening when Morrell was brought down just outside the box on the left.
A short free-kick was taken and when the ball eventually reached Shaughnessy, his shot had to be clawed away by Stryjek.
The display of eight additional minutes raised hopes of turning one point into three, but it looked as though the chance had gone when Bishop could not keep his header down from a Sparkes corner.
There was still time, however, as another Sparkes flag-kick was sent into the mixer and SHAUGHNESSY rose above Stryjek to head home.
Pompey (4-2-3-1): Norris; Rafferty, Poole, Shaughnessy, Sparkes; Robertson (Raggett 90+9), Morrell (c); Lane (Whyte 78), Anjorin (Saydee 56), Kamara; Bishop
Goals: Bishop 58, Shaughnessy 90+8
Booked: Robertson, Poole
Subs not used: Schofield, Swanson, Stevenson, Devlin
Wycombe (3-4-1-2): Stryjek; Forino, Keogh, Leahy; Pattenden, Scowen (c), Potts, Boyes (Tafazolli 66); McCleary (Sadlier 90+4); Hanlan (Phillips 80), Vokes (Taylor 66)
Goals: Scowen 22
Booked: Scowen, Leahy, Hanlan, Tafazolli
Subs not used: Ravizzoli, Low, De Barr
Referee: Alan Young
Attendance: 17,450 (277 away fans)