Pompey received a second successive slice of misfortune as they lost out to a fluke goal at Wycombe.
After being frustrated by a ricochet against Exeter last week, it was a wicked deflection that saw Scott Kashket claim all three points for the Chairboys.
Both sides created chances in a lively encounter at Adams Park, but it was the hosts who were able to boost their promotion credentials.
Paul Cook made five changes from the side beaten at home by the Grecians the previous week.
Eoin Doyle came straight into the starting 11 following his deadline day loan arrival from Preston.
Behind him was a new attacking trio of Kyle Bennett, Gary Roberts and – making his full debut – Jamal Lowe.
There was also a space for Amine Linganzi in midfield, while Conor Chaplin, Carl Baker, Kal Naismith and Danny Rose all dropped to the bench.
Pompey came roaring out of the blocks and Roberts slipped the ball through to Lowe, who could only drag the ball wide in the opening seconds.
But it was the hosts who then started to dominate, with the giant frame of Adebayo Akinfenwa unsurprisingly causing a few problems.
For all their balls into the box, however, there was little to trouble David Forde between the Blues’ sticks.
Christian Burgess did particularly well to beat Kaskhket to Akifenwa’s flick and powerfully head clear.
The centre-back then tried his luck at the other end of the pitch and met two Roberts corners, but sent one straight at Jamal Blackman and the other wide of the post.
Pompey started to look the more threatening side as the first half progressed and Eoin Doyle was unable to beat the Chairboys keeper after taking a fine touch to beat Anthony Stewart.
They had an even better chance to break the deadlock on 33 minutes when Bennett sent Enda Stevens through on goal, but Blackman came racing from his line to deny the left-back.
But the Blues survived a nervy moment just before the break when Matt Clarke and Stevens combined to bring down Kashket on the edge of the box.
It was the Irishman blamed by referee Graham Salisbury and shown a yellow card, but Sido Jombati’s free-kick was poor and comfortably claimed by Forde.
Wycombe Wanderers 0
Pompey enjoyed some joy at the start of the second half, with Eoin Doyle showing neat footwork down the left.
But the large band of travelling supporters saw their side fall behind in unfortunate fashion just moments later.
Forde dived to his left to keep out a routine shot from Kashket, but the ball took a massive deflection to leave the keeper stranded.
And the keeper then had to scramble back quickly to stop Burgess heading into his own net just a few seconds later.
Bennett tried to catch Blackman out at his near post when the Blues won a free-kick on 52 minutes, but the ball flew narrowly past the post.
The winger then whipped in a cross following a spell of patient build-up play, although there was nobody to meet it at the back stick.
Pompey were dominating possession by this point, with Wycombe doing most of their attacking work on the break.
Bennett played a neat one-two with Roberts on 67 minutes, but his low cross did not quite sit up right for Eoin Doyle in the box.
Cook made a double switch soon after in the hunt for an equaliser, with Lowe and Bennett withdrawn for Baker and Naismith.
And it was Baker who came close to immediately grabbing a goal, taking advantage of a mix-up at the back and hooking narrowly over.
Blackman then did well to stop Eoin Doyle netting from a tight angle, while Baker drilled an effort just past the post.
Chaplin was thrown on for the closing stages as Pompey poured forward and a display of eight additional minutes sparked hopes of a point.
Stevens, Baker and Chaplin all went close as the seconds ticked down, but the Blues were unable to salvage anything.
Wycombe (4-3-3): Blackman; Jombati, Stewart, Pierre (De Havilland 60), Jacobson; O’Nien, Gape, Wood; Kashket (Thompson 89), Akinfenwa, Hayes (c) (Saunders 46)
Goals: Kashket 48
Booked: Wood, Stewart, Saunders, Kashket
Subs not used: Richardson, Bean, Weston, Jakubiak
Pompey (4-2-3-1): Forde; Evans, Burgess, Clarke, Stevens; Linganzi, M.Doyle (c); Lowe (Baker 72), Roberts (Chaplin 86), Bennett (Naismith 72); E.Doyle
Subs not used: O’Brien, Whatmough, Rose, Hunt
Referee: Graham Salisbury
Attendance: 6,028 (1,800 Pompey fans)