There have been plenty of assured defensive displays to help Pompey reach the League One summit.
But they were exposed at the back on two occasions early in the second half to ensure Burton left Fratton Park with a point.
Devante Cole cancelled out Oli Hawkins’ header in the second half, while Jake Hesketh wriggled through moments later to turn the contest on its head.
Matt Clarke converted a corner to secure a share of the spoils, but the centre-back knows they have to do better at the back.
He said: “We were in control for large parts of the game, only to concede two goals in a short space of time and that ultimately cost us.
“I suppose it’s a bit out of character for us – that hasn’t really been how we’ve played so far this season.
"If it happens again then it becomes a problem, so we’ve got to nip it in the bud and make sure it’s a one-off."
“But it does happen at times and we at least reacted well to falling behind and were able to bring it back to 2-2.
“The midfield runner caused us problems for the first goal and then for the second, their guy just skips past too many people.
“Those guys have all put their hands up in the dressing room and admitted that it wasn’t good enough. We all know that.
“It’s not like Burton had loads of chances, but they’ve taken advantage of the ones they had because of our mistakes.
“If it happens again then it becomes a problem, so we’ve got to nip it in the bud and make sure it’s a one-off.”
Clarke rose highest in the box to meet Gareth Evans’ corner just before the hour mark and score his third goal of the season.
He said: “It was a good ball in and I was able to get up fairly early to meet it – it was quite simple from there.
“We have a lot of set-pieces and that’s a big part of football – the gaffer says it’s a game within a game.
“It’s something we’re looking to add more goals from and it’s pleasing that one’s come about on this occasion.”