Paul Cook admitted Pompey deserved their Crown Ground defeat as their winning streak ended.
Paddy Lacey’s superb 52nd-minute goal settled matters as Accrington clinched a 1-0 victory in a match of few chances.
Cook’s side had headed to Lancashire on the back of four successive victories, yet couldn’t even muster an attempt on target against Stanley.
It was a puzzlingly lacklustre showing from the visitors, who struggled throughout.
And their manager was under no illusions they got the result they warranted.
Cook said: ‘Very disappointing, we never played well, we never got going, we never had any real tempo about us.
‘Accrington were good, you have to give them credit, I am not just going to speak bad about us.
‘There are two teams in the game – and for me we were the second best today.
‘We have to be better today, come on. We’ve had good support travelling and we weren’t at it, we weren’t good.
‘I am disappointed for our fans but you go again, these seasons in these leagues can be tedious at times and tonight is one of those nights for us.’