Guy Whittingham was left looking for answers from his players in the wake of their 1-0 loss at Oldham.
A slow start to the League One contest at Boundary Park cost Pompey the only goal of the game.
Jose Baxter was allowed to run unchallenged and fire a low shot past Simon Eastwood from long range.
While the goalkeeper was at fault, Whittingham was fuming at the way his players made such a lacklustre opening.
And the caretaker boss admitted he was at a loss to explain it.
Whittingham said: ‘You prepare and you tell them to go and press the ball.
‘You tell them to get at them because they might have another game on their mind – with the FA Cup game against Everton tomorrow night.
‘So you tell them to get in their faces and to put them under pressure but we didn’t do it. I just don’t know why.
‘You remind them, you show the analysis.
‘You talk to them at the hotel, you talk to them before the game and you hope that they go out and do it. It didn’t happen.’
While Whittingham accepted Eastwood’s error for the goal, he also pointed to some fine saves the keeper may afterwards.
The Blues boss said: ‘Simon has kept us in the game many times.
‘He made a couple of great saves in the second half.
‘Unfortunately, it has happened to him.
‘But when you are a goalkeeper, if you make a mistake, they are usually costly.
‘He made a mistake, he knows it and we move on.
‘But we’ve conceded the goal in the first 10 minutes or so.
‘I’m concerned about why we have started the game like that.’