The pressure cranked up on Kenny Jackett as Pompey fell to a 1-0 defeat at AFC Wimbledon.
Terell Thomas’ late, late header meant the Blues suffered a last-gasp defeat against the struggling Wombles at Kingsmeadow.
Pompey yet again lacked cutting edge, having numerous chances in the first half but failed to score for successive games.
And they were made to pay in stoppage-time, with Wimbledon piling more misery on Jackett.
Pompey made three changes from last weekend’s 0-0 draw with Gillingham.
John Marquis again spearheaded the front line in place of Ellis Harrison, while Ryan Williams came in for the injured Brett Pitman.
Craig MacGillivray was also back in goal after returning from Scotland duty, with Alex Bass dropping to the bench.
Jackett’s side went close to breaking the deadlock in just the second minute when a Sean Raggett header from a corner was cleared off the line.
On eight minutes, Marquis brought down Evans’ cross from the right but stabbed wide.
There was a scare for the Blues four minutes later when Marcus Forrs skipped past Raggett and burst through on goal, only for Lee Brown to make a crucial block and steer the striker's shot over the bar.
In the 18th minute Marquis squandered a glorious opportunity. The big-money summer signing was set free by Marcus Harness but dragged his left-footed shot narrowly wide.
Pompey started to enjoy a sustained spell of pressure, with Ryan Williams shooting down home keeper Nathan Trott’s throat, while Tom Naylor headed over.
And on 27 minutes Christian Burgess crashed a headed off the crossbar from Brown's inviting cross.
Yet the centre-back almost gifted the Wombles an opened three minutes before half-time when he misjudged a bouncing ball and Joe Pigott’s lobbed effort went agonisingly wide.
Pompey went up the other end and Evans forced a good stop out of Trott when he was set free by Harness.
There was a heart-in-the-mouth moment for the visitors four minutes into the second period. Evans’ misguided header found Pigott and he was felled on the edge of Pompey's box by Burgess.
Forrs’ effort beat the wall but MacGillivray made a fine stop to his right to keep out the effort.
Jackett made a double substitution in the 57th minute as he looked to find a breakthrough, with Harrison and Ronan Curtis replacing Williams and Marquis.
Harrison’s pressing almost paid dividends when he charged down a Trott clearance, only for the ball to roll narrowly wide.
In the 65th minute Anthony Wordsworth must have thought he’d given the Wombles the lead when he sweetly caught a half-volley but it cannoned off the inside of the post.
On 71 minutes Naylor tested Trott when his powerful long-range effort was well held.
Close had an attempt saved in the 86th minute – and there was to be one moment of drama in stoppage-time.
Max Sanders’ 93rd minute free-kick was met powerfully by Thomas, who snatched the points for the home side.
That incensed some members of the 712 members of the travelling Fratton faithful, directing their ire towards the boss chanting “We want Jackett out”.
It means the Blues have picked up 13 points from just 11 games as their lacklustre form continues.
Pompey: MacGillivray, Bolton, Raggett, Burgess, Brown, Naylor, Close, Williams (Harrison 57), Evans, Harness (Cannon 83), Marquis (Curtis 57).
Subs not used: Bass, Haunstrup, Downing, McCrorie.
AFC Wimbeldon: Trott, Kalambayi, Delaney, Thomas, Wagstaff, Pinnock (Harigan 77), Sanders, Wordsworth, Oswe, Pigott, Forss (Apphiah 84).
Subs not used: Tzanev , Stabana, Guinness-Walker, McLoughlin, Madelin.