Michael Appleton admitted Pompey’s abject start left them too much ground to gain as Wycombe pulled off a shock 3-1 victory.
The League Two strugglers knocked the Blues out of the Johnstone’s Paint Trophy last night.
The foundation for that triumph was the opening 17 minutes of the Fratton Park encounter.
Joel Grant netted after just 13 seconds, while Dean Morgan made it 20 on nine minutes.
In addition, Jo Kuffour twice struck the left-hand post as Pompey wilted under some intense pressure.
Conceding the first goals in matches this season has been a recurring theme for the Blues.
Izale McLeod pulled one back on the stroke of half-time, before Morgan’s second after the interval settled matters.
And Appleton conceded that early collapse ultimately proved costly.
He said: ‘I say it every week – score the first goal and it gives you an opportunity to win games.
‘Mind you, not conceding two in the first 10 minutes also gives you an opportunity to win the game.
‘You fight an uphill battle as soon as that happens and it sets the tone.
‘Sometimes in football you have a feeling. When I saw that go in and then the second go in I just knew.
‘The atmosphere was a little bit funny as well.
‘It certainly gave us an uphill battle but we did have a lot of opportunities to get back into it and I thought we were sloppy in front of goal.
‘We never created a bundle of clear-cut chances, but there were opportunities.
‘The amount of times we got into their box and made the wrong decision was a little bit disappointing.
‘My players had a go at it and tried to get back into it and I think if we had got our second goal we would have gone on to win the game – although that is me being slightly biased.
‘Still, the one thing we need to improve on is coming out of the blocks quicker.
‘We did that to MK Dons last weekend and went two up.
‘Then Wycombe did it to us last night and we didn’t have enough in the locker to get back.’
To cap a frustrating night for Pompey, Lubomir Michalik came off in the second half with a tight calf.
Meanwhile, Mikkel Andersen was rested to give Simon Eastwood his Fratton debut.
Appleton is now looking for Pompey to put the disappointment behind them, with Crewe next up in the league on Saturday.
He added: ‘I am not going to draw too much from this. It is a competition that would have been nice to go through to the next round.
‘But come today I couldn’t care less, it is more important what happens on Saturday.
‘It was Wycombe’s night, they came here, had a fantastic start to the game and played well. Good luck to them.
‘This is a match where we need to move on very, very quickly.
‘Winning last night is 10 times less important than picking up three points on Saturday against Crewe.’