Michael Appleton admitted the abject Ricoh Arena display represented his lowest Pompey ebb.
The Blues choked against their relegation rivals on Saturday in a crucial fixture.
Coventry ran out comfortable 2-0 victors as the visitors failed to build on the outstanding romp over Birmingham last week.
Chris Maguire struck the inside of the post with a free-kick, while Luke Varney missed a glorious headed chance from close range.
Yet Pompey fans can have no complaints over the result as Andy Thorn’s side ran out deserved winners to surge five points ahead in the fight for survival.
And for a seething Appleton, the showing surpassed even his woeful first match at Watford earlier in the season.
He said: ‘We didn’t deserve to get anything out of it and probably it is my most disappointing game so far.
‘Mind you, you would have to go a long way to be more disappointed than my first game in charge (Watford).
‘This did, though, just because of the circumstances.
‘It’s just a missed opportunity.
‘There are still going to be plenty of opportunities over the next five or six weeks but if it was a test – back at school – we failed this one.
‘You could use the excuse our players were a little bit leggy and games had caught up with them but Coventry played after us on the Wednesday, so we can’t even use that as a reason.
‘I wasn’t happy with it and sometimes you can show your emotions after the game.
‘But sometimes you have got to take stock and look at the bigger picture and the bigger picture is we have got two really important games coming up.
‘If I showed too much frustration from Saturday’s game and can’t get it out of my head, then I am not concentrating enough on the forthcoming games – which are coming thick and fast.
‘You have got to take opportunities – there are not enough games left.
‘Hopefully the disappointment will trigger something over the next eight games.
‘The next two games being at home could make the difference to what finally happens at the end of the season.’
Gary McSheffrey and Oliver Norwood scored the second-half goals which condemned Pompey to defeat. It leaves Appleton’s men six points adrift of safety with eight matches remaining.
He added: ‘We had the better of the first half in terms of possession but never moved the ball quick enough.
‘The first half to me was almost like a testimonial pace at times.
‘We just didn’t get after them as early as I wanted – especially after the second-half performance on Tuesday – and we paid the price.
‘We made wrong decisions in and around the edge of box.
‘Players passed on responsibility far too much.’