Guy Whittingham admitted he was ‘baffled’ over the abject first-half display which laid the foundations for a seventh successive defeat for Pompey.
The Blues shipped three goals in an appalling opening 20 minutes against Colchester on Saturday to leave them 3-1 down.
Gavin Massey grabbed two of them and could comfortably have had a hat-trick as the hosts clung on until the break.
Pompey were unrecognisable in the second half, with an upbeat attacking performance that allowed James Keene to pull a goal back.
Nonetheless, it finished in a 3-2 defeat for Whittingham’s men – making 17 matches without a win.
After an encouraging and committed display against Notts County in the week, the first half against the U’s was a shock to the caretaker boss.
And Whittingham was left scratching his head over the possible reasons behind it.
He said: ‘It is baffling, you just don’t know why that is.
‘Obviously it’s a mental side of the game that players have to have – but on Saturday it just wasn’t there.
‘You try to think when you are a player that all you are worried about is that 90 minutes on the football pitch, to do your best, to commit to things and they didn’t on Saturday.
‘We have got to put that behind us now and go into the next game tomorrow night. We just need to remind them about the second-half performance on Saturday.
‘That’s what people want to see – players committing to the runs, to the balls, to the tackles, to the headers, everything.
‘It was just a chalk and cheese performance.
‘I remember at one point Johnny Ertl winning the ball a few times in midfield and it was fantastic.
‘That is what the fans want to see.’
Poor defending has long been a characteristic of Pompey this season, with just three clean sheets in 33 games.
Saturday was no different in that opening 20 minutes, as Massey’s double and a Freddie Sears penalty gave the visitors an unassailable advantage.
Sandwiched among that lot was Jed Wallace’s second goal for the Blues, netting from Dan Butler’s corner.
Afterwards Whittingham chose not to pinpoint players individually for criticism in that hapless start to the Fratton Park fixture.
He said: ‘When you are looking at defenders you can’t say any of our goals were one person’s fault.
‘There are two or three people at fault slightly which leads to the goal.
‘The first goal was like the other night. A decent cross and Sodje could have been in the right place but the lad has made a great run, taking Yassin Moutaouakil one way and then driving inside him.
‘With the second, I think the referee was giving those decisions all afternoon – some thought they were fouls, others thought they weren’t.
‘There were a couple of handballs he gave the wrong way but it’s not his fault we lost 3-2.
‘The third was a wicked deflection and then Liam Walker had one second half which took a deflection and went over the bar.
‘There you go.’