Pompey have made a solid start to the League One campaign.
In fact, only Barnsley can boast a better defensive record after the opening five fixtures of the 2018/19 season.
The recently-relegated Tykes have conceded just twice, which is one fewer than the Blues have let in.
And Matt Clarke believes that impressive record is at least partly down to having such a settled back-line.
He said: “We conceded too many goals for our liking last season and it’s something we’ve definitely worked on.
“You can see that resilience in the results so far, but it’s no use just talking about it, we have to keep it up for the whole season.
"We conceded too many goals for our liking last season and it’s something we’ve definitely worked on."
“Whoever plays, we feel like we understand each other’s game and know the way we’re trying to defend.
“That’s true whether I’m with Jack Whatmough or Christian Burgess – or whether those two play together.”
Pompey will look to continue their unbeaten opening to the season when they host Plymouth on Saturday.
Clarke said: “Those who have played against them in recent seasons will know they always seem to be good games.
“The fans enjoy them and we do as well. It’s going to be a decent test and one that I’m looking forward to.
“It’s nice to have a few matches at Fratton Park now following a couple on the road, so it’s important we take advantage of that.
“You always check the table when you’re winning games on the bounce and it’s nice to be up in the mix – hopefully we can stay there.”