Ten-man Pompey slumped to a 1-0 defeat at Oldham as their wretched winless run was stretched to 22 matches.
Guy Whittingham’s men fell behind to Jose Baxter’s 11th-minute strike from distance which was misjudged by Simon Eastwood.
It proved to be a crucial error by the keeper as Pompey could find no way back against their fellow strugglers.
Sam Sodje’s 50th-minute dismissal following a clash with Lee Barnard hampered them further, a needless off-the-ball sending-off witnessed by the linesman.
As Oldham pushed, Jonathan Grounds struck the far post with a free-kick on 71 minutes, while Jordan Obita’s overhead kick hit the other post within minutes.
Yet it ended 1-0 to Oldham, leaving the visitors still without a victory since October 20.
Whittingham made four changes to the side which lost to Carlisle last weekend, with Gabor Gyepes among those recalled.
Yassin Moutaouakil, Liam Walker and John Akinde were also back in the starting line-up, the injured Shaun Cooper, Ricardo Rocha, Adam Reed and James Keene missing out.
When the match got under way, an error in judgement from Eastwood allowed Oldham to take the lead in the 11th minute.
Baxter brought the ball forward and drove in a low shot from 25 yards which went under the dive of Eastwood and into the net.
Moments later Sodje missed a long bouncing ball down the middle but Barnard’s lob was safely gathered by Eastwood.
Pompey had their first effort on goal in the 16th minute when Akinde’s stooping header from Patrick Agyemang’s cross was stopped by Dean Bouzanis.
A mistake from Moutaouakil almost gifted Obita a goal and then Lee Croft drove an effort from distance just over the bar.
At the other end, a rare Blues attack saw the ball fall to Akinde, whose original shot was blocked by James Tarkowski and his follow-up was a wild overhead kick which screwed wide.
In the 50th minute Pompey were reduced to 10 men when Sodje was shown a red card after the linesman witnessed an altercation with Lee Barnard.
Grounds’ free-kick from the right then struck the far post as Pompey survived once again.
Moments later Obita struck the other post with an overhead kick and Eastwood had to then produce a smart save to deny Barnard.
There were five minutes added on but Pompey could not create the equaliser as they fell to another defeat.
OLDHAM 1 (Baxter 11)