Adam Phillips scored the only goal as Portsmouth were denied a play-off place after losing 1-0 at home to mid-table Accrington.
Pompey had to better Oxford and Charlton’s result to cement their place in the top six but were made to pay for a lamentable first-half display by being consigned to another season in League One.
Accrington took the lead in the 23rd minute when Phillips played a neat one-two with Harvey Rodgers before firing the ball high into the net.
Phillips was close to doubling his and the visitors’ tally six minutes later when his 30-yard free-kick was magnificently pushed around the post by Craig MacGillivray.
Pompey were much improved in the second half and Ronan Curtis and George Byers both called goalkeeper Toby Savin into action as they pushed for an equaliser.
Savin made another good stop five minutes from time to deny substitute Charlie Daniels from close range before making a flying save to keep out Curtis’ stoppage-time free-kick.