Marcus Harness netted his seventh goal of the season as Pompey earned a hard-fought victory at high-flying Wycombe.
The forward bundled the ball home after good work from Ronan Curtis and George Hirst to secure the points.
Alex Bass had earlier saved a poor penalty from Joe Jacobson to ensure the sides went in level at the break.
And the Blues had to survive a torrent of late pressure before the noisy travelling army were able to celebrate.
Danny Cowley made three enforced changes from the side that beat Harrow Borough in the FA Cup the previous week.
With Gavin Bazunu and Joe Morrell both away on international duty, Bass and Louis Thompson came into the starting line-up.
The other switch saw Hirst – fresh from his Papa John’s Trophy heroics – replace the injured John Marquis up front.
Reeco Hackett is also nursing a knock, as three members of the academy side occupied spots on the bench.
There was also an alteration to the formation, with Harness playing behind Curtis and Hirst at the tip of a diamond midfield.
The first half was an absorbing – often frantic – affair, with both sides causing problems going forward.
And the trickery of Harness drew an early foul from Jordan Obita that saw the former Fratton loanee receive a yellow card.
But the Wycombe winger was soon causing trouble of his own and fired in a low shot that struck the outside of the post.
A chance for Brandon Hanlan also rolled harmless wide, while strong defending from Anthony Stewart at the other end prevented Curtis from getting on the end of a Harness delivery.
Hirst was proving to be a lively presence up front and an effort from the edge of the box rolled past the post.
Bass then launched an attack after claiming a Jason McCarthy cross and when the ball eventually landed for Harness, he fired wastefully over.
There was a spot of controversy when Thompson took a tumble over Obita inside the area, only to have his penalty appeals waved away by referee Neil Hair.
And the mood did not improve when Anis Mehmeti collided with Sean Raggett and the Blues defender was deemed to have committed a foul.
Jacobson stepped up to take the penalty, but hit the ball straight down the middle and Bass made the save.
Pompey’s bench were raving about the two decisions, with both of the Cowley brothers being booked.
Hirst had a chance to get the visitors on top after racing onto a precise long pass from Shaun Williams.
He did well to hold off the challenge of Ryan Tafazolli and get past the defender, but David Stockdale dived at the striker’s feet to claim the ball.
Half Time: Wycombe 0 Pompey 0
The Blues almost broke the deadlock soon after the restart when Harness slipped a neat pass through to Hirst.
It was a clean strike from the Leicester loanee, but Stockdale made a superb save to push the ball over.
And there was another opportunity from the resulting corner that was whipped in by Miguel Azeez, but Raggett could not quite keep his header down.
It was a similar story again a few moments later, although this time the centre-back nodded the ball downwards and it bounced wide.
The Chairboys had a chance of their own just before the hour mark, but Mehmeti’s fierce strike was beaten away by Bass.
Pompey were certainly looking capable of scoring and a teasing Curtis cross was just out of reach for Hirst after the Republic of Ireland international had been found by a fine Harness pass.
Curtis then had a chance of his own, but his angled shot flew agonisingly past the post, with Stockdale perhaps getting his fingertips to it.
Cowley made a switch on 68 minutes, providing a midfield refresh by replacing Azeez with Michael Jacobs.
Thompson then did well to surge forward in the centre of the pitch and find Harness, whose low shot was spilled by Stockdale, but grabbed at the second attempt.
And the goal the visitors deserved did arrive on 73 minutes after Curtis sent a fine pass down the left.
That sent Hirst racing clear and he unselfishly squared for HARNESS, who took a poor first touch, but slid in to make sure the ball crossed the line.
Wycombe threw on former Blues winger David Wheeler and Adebayo Akinfenwa in an attempt to find a leveller.
And the latter soon had a chance to score, but could not keep his header down from an Anthony Stewart centre.
The hosts were forcing plenty of late pressure on their opponents, which led to a few nervy moments.
Hirst received a standing ovation for his tireless display as he made way for Gassan Ahadme for the closing stages.
But it looked like Wanderers had levelled late on when McCarthy’s shot hit the inside of the post and his follow-up was blocked by Raggett.
Six minutes of stoppage-time lifted the home side’s spirits, but Bass made a brilliant save to keep out Sam Vokes’ header at the death.
He then did the same again, this time to deny Akinfenwa from point-blank range and ensure the Blues would depart with all three points.
Wycombe (3-4-3): Stockdale; Stewart, Tafazolli, Jacobson (c) (Wheeler 76); McCarthy, Thompson, Scowen, Obita; Mehmeti (Akinfenwa 76), Vokes, Hanlan
Booked: Obita, Jacobson, McCarthy
Subs not used: Przybek, Grimmer, Forino, Pendlebury, Parsons
Pompey (4-1-2-1-2): Bass; Romeo, Raggett, Ogilvie, Brown (c); Williams; Thompson, Azeez (Jacobs 68); Harness (Downing 90); Hirst (Gassan 86), Curtis
Goals: Harness 73
Subs not used: Steward, Freeman, Kaba, Hughes
Referee: Neil Hair
Attendance: 6,471 (1,420 Pompey fans)