Pompey turned in one of their poorest displays of the season as they slumped to a 1-0 loss at AFC Wimbledon.
The winner came just six minutes into the contest as Craig Tanner’s shot was deflected into his own net by Ben Chorley.
While the shot looked goal-bound before Chorley got a touch, the striker got through far too easily in the first place to get his effort away.
In response, Pompey had to wait until the 40th minute before Matt Tubbs’ header was well saved by Ross Worner after Jed Wallace’s cross was fired in.
With Blues fans expecting a backlash after the break, it never materialised and Wimbledon looked the more likely to add further goals.
Paul Jones made some good saves and Adebayo Akinfenwa saw a header clip the top of the crossbar.
While boss Andy Awford threw all his strikers on with the game drifting away, a tame header from Paul McCallum was their only real sight of goal in the second half as they surely waved goodbye to any forlorn hopes of making the play-offs.