It’s the key to the entire club’s fortunes, according to Michael Appleton.
And Pompey’s boss has warned Josh Thompson and Adam Webster they are not yet ready to be handed such a responsibility.
Appleton has been forced to audition many candidates in the centre of defence during the opening month-and-a-half of the season.
Now Lubomir Michalik and Gabor Gyepes appear to be the settled pairing in his starting line-up, serving alongside each other for the past two matches.
So far their partnership has been in defeats to both Swindon and Notts County, conceding five goals in the process.
Nonetheless, Appleton considers them his favoured centre-half double act in his current squad.
That has left Thompson on the bench after twice featuring there, in addition to a second-half switch from full-back to the centre against Crawley.
Meanwhile, Webster has been used solely as a right-back, making two starts and three substitute appearances so far this campaign.
The Blues boss sees both as having long-term roles to play in the heart of his defence. But not just yet.
He said: ‘Probably the key position in the whole club is your centre-half pairing.
‘The centre-half pairings we have had, we have got and have to have is certainly slightly different to the one I thought I would have in May, let’s put it that way.
‘Now we have got two players there (Michalik and Gyepes) with enough experience and enough about them.
‘I just hope and pray they can stay in there for five or six games and that will give me a lot more comfort.
‘Josh is a young kid. You can tell he has not had a lot of football straight away.
‘He is a big lad and he needs to use his body better, which I have no doubt he will do over time.
‘The unfortunate thing for him is that he needs games.
‘The position we are in at the minute, can we afford to keep playing someone and giving them games for their education, in terms of building them as a player, when we are trying to fight for points for our lives?
‘We have got to get that balance right with Josh and will do that as best as we possibly can.
‘In an ideal world – if there is a takeover and we can strengthen the squad as utmost as we can – then if it’s a situation where he can be part of what we are trying to do here and we can possibly, possibly send him out on loan somewhere then fine. If not, we keep him here and work with him every day. After all, he is only 21.’
Webster is another natural central defender.
The 17-year-old, however, has been earmarked for a full-back role until the time is right.
For that very reason, Appleton will be keeping him away from the central-defensive areas in his team in the immediate future. Pompey’s manager added: ‘We are also trying to protect people like Adam Webster in the same breath.
‘Eventually he will be a centre-half but that is why we have only used him as a full-back at the minute.
‘I have no doubts that Adam will be down as a centre-half at some point.
‘But at the minute, when he gets his opportunity, it is more than likely to be as a full-back.’