Pompey have effectively been condemned to another season in League One after falling to a 1-0 defeat against Charlton at Fratton Park.
Nicky Ajose’s first-half goal means Kenny Jackett’s side’s play-off ambitions suffered a huge blow, with the Blues paying the price for being weaker in every department against their top-six rivals.
Pompey were indebted to Nathan Thompson in the 21st minute when he made a goal-line clearance.
Jake Forster Caskey’s shot inside the box beat keeper Luke McGee but the right-back hooked away the goal-bound effort.
Thompson again had to make a crucial intervention seven minutes later when Tarique Fosu-Henry was left in space at the back post, but the former Swindon captain’s stretching block thwarted the effort.
The Blues had claims for a penalty in the 35th minute when Jason Pearce appeared to be pull Brett Pitman’s shirt.
But the inevitable Charlton opener came five minutes before half-time.
Josh Magennis’ cross picked out Ajose, who tucked his effort home when one-on-one with McGee.
Jackett made a tactical change at the break, with Christian Burgess and Stuart O’Keefe replacing Jack Whatmough and Nathan Thompson.
And Pompey should have been level three minutes into the second half when Pitman wasted a gilt-edged opportunity.
Gareth Evans’ free-kick from the right found the Blues captain six yards out, but he steered his left-foot shot over the bar.
Pitman then fired over on the spin four minutes later.
On 59 minutes, Ben Reeves’ long-range shot whistled just past the post, while Burgess made a crucial block to deny Ajose a second.
Pompey continued to push for a leveller, though, with Charlton keeper Ben Amos producing two decent saves from Pitman and substitute Connor Ronan.
The captain was then handed the opportunity to rescue his side a point with a free-kick from 25 yards, but Amos beat the effort over the bar.
Although mathmatically still possible, the play-offs look a long way off now.
The Blues trail sixth-placed Scunthorpe by four points, with the Iron playing one game fewer.