Miles Storey struck the only goal of the game as Pompey clinched a place in the second round of the Capital One Cup with a victory over Peterborough.
The on-loan Swindon forward drove home a crisp effort with just 12 minutes on the clock, after he jinked in the inside right channel and found the bottom corner with accuracy.
Peterborough offered very little in the first half, with Blues keeper Paul Jones untroubled.
And while the League One club upped the tempo after the break, Pompey turned in a fine defensive display with a new three-man central defence that worked well.
Craig Westcarr thought he had given Pompey breathing space with a second goal, only to be denied by the referee’s whistle for handball.
And although Posh’s search became increasingly desperate, Pompey stood firm and saw out an inexplicable six minutes of stoppage-time to secure their passage into the next round.