Stuart O’Keefe admitted Pompey’s failure to come to terms with their system change hampered their Rotherham showing.
Kenny Jackett handed starts to two of his deadline-day signings in addition to introducing a 3-4-1-2 system for the televised clash against the Millers.
There’s things to work on, we know that, the manager knows that and we will get betterStuart O’Keefe
The outcome was the formation being scrapped at half-time, with the Blues subsequently slumping to a first home defeat of the season.
O’Keefe joined Oliver Hawkins in making his Blues debut following their arrivals on a busy Thursday end to the transfer window.
The Cardiff loanee occupied a central midfield role ahead of a back three comprising of Christian Burgess, Jack Whatmough and the fit-again Matt Clarke.
The former Crystal Palace man caught the eye in his maiden Pompey outing, as did fellow Bluebirds newcomer Matty Kennedy from bench.
But first-half problems with the new system was obvious in the 1-0 defeat to Rotherham
And the straight-talking O’Keefe revealed his team-mates struggled to adjust to their new set-up.
He said: ‘It was a poor result, we are a lot better than that.
‘We looked a bit disorganised and unsettled – possibly that was down to the system.
‘We are a young squad with some new faces in there. To change formation is going to be difficult for the boys to adapt to, especially with the atmosphere live on the box. We are a team learning.
‘With the deadline now over, now with our time together, and nobody coming in or out, the squad will work on it on the training ground and in the games. We will be okay.
‘Changing formation is not that simple, I wish it was.
‘Unfortunately, we also played against some good players at a good level who made it difficult.
‘Rotherham got their goal and that was it. They had something to hold onto and sat behind the ball, and it’s up to us to come up with something and be better than that.
‘In the second half we played a little bit more on the front foot and were a threat with the wingers.
‘We didn’t have enough shots on target, their keeper didn’t have to make too many saves, but we looked a little bit more of a threat.
‘I think we’ll be okay in time. There’s enough here to kick on up the league where we should be.
‘There’s things to work on, we know the manager knows that and we will get better.’
The match represented a first league appearance of the campaign for O’Keefe, having fallen out of favour under Neil Warnock at Cardiff.
He did, however, start both of the Bluebirds’ Carabao Cup fixtures last month, one of which came in the 2-1 extra-time victory against Pompey.
O’Keefe impressed on his Fratton bow and, although he believes he is still feeling his way into his new club.
He added: ‘I had one training session with the team to prepare for the game, so am still finding my feet and getting to know everyone’s names.
‘Onwards and upwards, there’s a lot of games in the next couple of months, so we’ll get on with it and learn from it.
‘I have a lot more to offer and we can kick on and get up this table.’