Kenny Jackett admitted he is still searching for his best centre-half combination after Pompey’s defensive capitulation to Coventry.
The Blues boss last night paired up Sean Raggett and Paul Downing for the first time in competitive action.
For the fit-again Raggett, it represented his full Pompey debut, selected ahead of Christian Burgess.
However, it was a match to forget as Jackett’s men conceded twice in the final 16 minutes against a Sky Blues side which finished with nine men.
Pompey’s rearguard looked frail throughout during the 3-3 draw – and Jackett was unhappy with how the centre-halves fared.
He said: ‘I went with Downing and Raggett to see how the combination worked.
‘With Raggett, I felt from set-pieces we needed that first header and wanted to give him an opportunity with Paul Downing.
‘I think he looked rusty, there’s a bit to come with him, but he hasn’t had much football and will come through it and have enough character to prove to be a good player.
‘Sean probably hasn’t played much football, that’s where it is. For him finding his feet and confidence at a new club is a big thing.
‘He will be disappointed and frustrated like all of us. We were in a really good position with a lead against 10 men – and then a lead against nine men. The nature of the goals were soft for us.
‘Obviously we don’t think we have the defensive unit right, whether that’s an individual, or whether the whole combination.’
Elsewhere in the Blues’ back line was Ross McCrorie, coming in for Anton Walkes at right-back.
While an Achilles injury to left-back Lee Brown saw him replaced by Brandon Haunstrup on 32 minutes.
It created an unfamiliar look to Pompey’s defence, although Haunstrup weighed in with an assist for John Marquis goal which earned the hosts a 2-1 lead.
And Jackett conceded the lack of familiarity among the rearguard may have had an impact.
He added: ‘I did feel for Ross, it was a tough start to the game, but he came onto it.
‘There were quite a lot of new lads there, as a unit trying to work together and to find their communication.
‘It wasn’t quite there, obviously, and then ultimately we’ve conceded three goals.
‘We still looked vulnerable because Coventry had a goal ruled out for offside as well. It was offside, but similarly it was a free-kick from left to right and their guy has come in on the far post and put it in.
‘Although it was offside, we didn’t necessarily play him offside, and that is still disappointing.’