Brandon Haunstrup wants Pompey to shake off any disappointment and try to end the season on a high.
Defeat to Charlton at Fratton Park means it is now extremely unlikely that the campaign will be extended by the play-offs.
Nicky Ajose struck late in the first half to ensure it was the visitors who boosted their own hopes of a top six finish.
Haunstrup admitted it was a poor performance from the Blues and wants to see an improvement in the remaining fixtures against Bury and Peterborough.
The full-back said: “We just want to get our heads down now and try our best to finish the season as strongly as we possibly can.
“There are two games left for us and we want to win both of them, so we can take some momentum into next season.
“I was pleased to be starting against Charlton, but my bigger focus was on the team because we all wanted to be in the play-offs.
"We just want to get our heads down now and try our best to finish the season as strongly as we possibly can."
“But the performance wasn’t really like us at all – we couldn’t really get going or get forward as much as we usually do.
“There were a few sloppy passes in the first half – well, quite a lot of them actually. We lost possession and couldn’t afford to do that against a side like Charlton.
“We had a few chances in the second half, although I don’t think we really created enough from open play to deserve to win.
“I think a lot of people would agree with that because although our opponents sat back, they pressed well and won a lot of battles in the middle third.”
Haunstrup is out of contact in the summer, although that has not been at the forefront of his mind in recent weeks.
He said: “There’s been a little bit of discussion, but the focus for everyone was on this season and doing our best for the club.”