Steve Evans believes Pompey punished the mistakes made by Peterborough.
Kenny Jackett's men moved the Posh off the top of League One with a 2-1 victory at London Road on Saturday.
Oli Hawkins fired Pompey in front on 62 minutes before Jamal Lowe doubled their advantage 13 minutes later.
Matt Godden bagged a consolation stoppage-time goal for the hosts.
However, Evans felt the goals Peterborough conceded against Pompey were preventable.
He told the Peterborough Telegraph: 'We left a man unmarked in the penalty area for the first goal and then lost the ball with a poor pass for the second goal.
'We lost because they took advantage of our errors.
'They didn’t make any in their own penalty area. We didn’t show any finesse or quality on the ball until it was too late.'
Although Godden netted goal for Peterborough, they also had a couple of other decent opportunities.
Ivan Toney was unable to convert Marcus Maddison's free-kick and also Siriki Dembele missed a last-gasp chance.
Evans insisted the pair should have done better.
The Peterborough manager added: 'We still had time to get back in the game.
'Ivan Toney should have scored from Marcus Maddison’s free kick and Siriki Dembele should have scored with the last kick of the game.'