Defeat at Bradford on Tuesday saw Pompey miss a chance to climb into the top six.
But Kenny Jackett has certainly not given up hope of them making the play-offs with three games remaining.
The first of those sees fifth-placed Charlton – who beat Shrewsbury in midweek – visit the south coast this weekend.
And Jackett knows that failure to collect a maximum haul of points will likely spell the end of Pompey’s promotion aspirations.
The Blues boss said: “We still see these last three games as very much an opportunity for us to get into the top six.
“In most games we’ve been within touching distance and certainly haven’t got blown away on many occasions.
"We’ve got a target of nine points against Charlton, Bury and Peterborough – we are capable of going on that run."
“But the bits we have to find in order to be one of the three sides promoted out of this division are key. We have to learn and learn quickly.
“We’ve got a target of nine points against Charlton, Bury and Peterborough – we are capable of going on that run.
“That would take us to 72 points, which is around where the play-off points tally usually starts. Whether that will be enough, I don’t know.”
Charlton’s campaign looked to be fading, but the appointment of former England international Lee Bowyer as caretaker manager last month seems to have revitalised them.
Jackett said: “They’re one of the powerhouse sides in this division and, like us, will have had aspirations of finishing in the top six all season.
“We’ll respect Charlton because they have many strengths, although we have to get our own game right.
“Both sides have been there or thereabouts right the way through the campaign, so we need to get our best form together.”
Pompey will still be without Anton Walkes, who has been sidelined for the past two matches with a hamstring problem.
Jackett said: “He won’t be fit this weekend, although we’ll see whether he’ll be ready within the next week or two.
“We’re hoping to have Matty Kennedy available for the weekend, though, and we’ll see on Friday morning whether he can make it back.”