Luke McGee rued the own goal which sent his side spinning to defeat at Peterborough.
Kal Naismith’s mistake made the difference as Pompey fell to a 2-1 loss at London Road.
That saw upwardly-mobile form stall after back-to-back league wins and three consecutive successes in all competitions.
Pompey are five points off the play-offs ahead of Saturday’s visit of Plymouth.
McGee refused to blame ill fortune on his team coming away empty-handed but still felt frustration at the manner in which the game’s decisive moment unfolded.
He said: ‘It was a good ball and it is frustrating it has ended up in the bottom corner.
‘I don’t think you can blame luck but Naisy gets his head on the second goal and a lot of the time it goes over the bar.
‘It’s not a lack of desire or willingness to fight. If no-one was going for that header we’d be asking questions.
‘Everyone wants to get their head on it and get there for the team, so it’s just one of those things.’
McGee was left disappointed in his hunt for an eighth clean sheet after a shut out against Southend at the weekend.
Christian Burgess’ fifth yellow card of the season means he will be missing against Plymouth on Saturday.
That means another reshuffle to Pompey’s defence – but McGee believes it is something Jackett’s squad can handle.
He said: ‘We had problems at the back with the injuries and people being unable to play.
‘But whoever’s at the back, has come in and done well.
‘Whoever’s at the back we feel is capable of keeping a clean sheet.
‘There’s character in the squad, so whoever comes in is more than capable.’