Kenny Jackett admitted his midfield is lacking power.
The Pompey boss pinpointed the middle of the park as the key area where the play-off showdown with Charlton was lost.
Jackett felt his central players failed to impact the 1-0 defeat.
Dion Dononue started centrally with Gareth Evans and Ben Close before Stuart O’Keefe’s half-time introduction.
Jackett feels Pompey have missed Anton Walkes strength since the Spurs loanee has been injured.
He said: ‘I thought their two midfielders were very good and had too much control of the game. That was the difference.
‘There were misplaced passes in midfield and it was an area we lacked in.
‘We wanted to use Dion’s left foot to get some longer passing and shots in.
‘He did some good things and some poor ones.
‘He looked more comfortable at left-back than in midfield, but, as a three we didn’t get hold of it in the first half.
‘The second period we didn’t really either.
‘I thought their midfielders were excellent.
‘Since we’ve lost Walkes we’ve lacked power in front of the back four.
‘It’s made us a little bit light in there physically.’
Jackett felt Charlton ultimately saw the game out without being stretched enough after taking the first-half lead.
He said: ‘They’ll be pleased as a defensive unit to keep a clean sheet, because it was key at a key time of the season.
‘They are probably in pole position in terms of the play-offs now at a key time of the season.
‘Despite our pressure in the second half they could edge us of.
‘It was close and I wouldn’t say there was a great big gap, but they edged it and done the job.
‘We struggled down our right-hand side. Nicky Ajose getting in was a problem. Jake Forster-Caskey and Lewis Page were distributing it. The first half was Charlton’s and they deserved it.
‘But they were only 1-0 up and we knew we could pull it back. There was time to go and we put pressure on them in the second period.
‘We made the game close but ultimately couldn’t do enough.’
Pompey will assess the injuries which forced off Jack Whatmough and Nathan Thompson at half-time on Saturday.
Jackett said: ‘Both players were injured and needed to come off at half time.
‘Whatmough was a groin injury and Thompson had a dead leg, but we can’t see how bad they’ll be at the moment.’
– JORDAN CROSS