The winger bagged the only goal of the game at Adams Park, after Alex Bass’ first-half penalty save from Joe Jacobson.
Pompey withstood pressure throughout from Gareth Ainsworth’s side, who posed a stern physical challenge.But Cowley’s men had chances themselves and stood strong through six dramatic minutes of stoppage time, to pick up the result of the season on the road on a afternoon of lively action.
Pompey made three changes from the FA Cup win over Harrow, as Alex Bass, Louis Thompson and the injured John Marquis replaced Joe Morrell, Gavin Bazunu and the injured John Marquis.
The Blues found themselves under intense early pressure from the home side with former loanee Jordan Obita cracking the post with a low drive after six minutes.
There were major fears over Alex Bass’ fitness with the keeper down and needing treatment, and 16-year-old Toby Steward on the bench. Bass was able to continue, though.
George Hirst’s renewed confidence was clear to see as he took on a 20-yard drive after 20 minutes which wasn’t far wide.
More decent play from Hirst five minutes later eventually saw the ball worked to Marcus Harness, who blasted over as David Stockdale narrowed the angle.
Pompey had a penalty appeal ignored for a foul on Louis Thompson, before a spot kick was controversially given moments later as Sean Raggett and Anis Mehmeti collided in the box.
The Blues fans behind Alex Bass’ goal were celebrating moments later, though, as he stood firm and held Joe Jacobson’s effort down the middle of goal.
Then Hirst got away from Ryan Tafazolli, but his chop took the ball into the arms of Stockdale.
Wycombe were indebted to Stockdale for keeping it level just after the restart, as he produced a superb save to his left to keep out Hirst’s 12-yard drive, with Raggett flashing a header over from the ensuing corner.
Bass then made a fine save to keep out the busy Anis Mehmeti’s angled drive after 58 minutes.
Pompey threatened with a lovely counter between Harness and Curtis, with the latter’s cross just in front of the on-rushing Hirst.
The breakthrough came with 17 minutes left as Curtis freed the lively Hirst, who burst through and crossed for Harness to bundle the ball home from close range.
Then it was a case of standing firm to a succession of balls into the box from the home side..
McCarthy cracked the post and then saw Raggett clear his follow up at the end of normal time.
Then Bass made two superb saves from Vokes and Akinfenwa in stoppage time to secure a huge win for Pompey.