Peterborough gave their League One promotion bid a welcome boost after back-to-back defeats with a 1-0 success that put another dent in managerless Portsmouth's play-off prospects.
The only goal arrived in the 32nd minute and it was one to forget for Pompey keeper Craig MacGillivray.
He was caught out by a goalbound Harrison Burrows corner and could only punch the ball against the back of defender Rasmus Nicolaisen for a calamitous own goal.
That proved enough for Darren Ferguson's men to halve the gap between themselves and leaders Hull to three points while also pulling four clear of third-placed Lincoln.
Pompey, under the temporary charge of Joe Gallen following the weekend sacking of Kenny Jackett, rarely looked like managing a reply as they slumped to a sixth defeat in their last eight league games.
Nicolaisen saw a shot bravely blocked by Mark Beevers before Jack Whatmough headed wide from a Lee Brown cross just before the hour.
Posh then looked likelier to extend their advantage with substitute Mo Eisa and Louis Reed both denied by MacGillivray before a last-ditch James Bolton challenge prevented Burrows from flicking in a Joe Ward cut-back.