Pompey boosted their hopes of finishing in the top two by securing victory at promotion rivals Peterborough.
It a close and tense encounter for much of the afternoon, with John Mousinho's men going close through Colby Bishop and Conor Shaughnessy.
Ephron Mason-Clark hit the woodwork for the hosts, but it was the visitors who took the lead when Gavin Whyte teed-up Kusini Yengi to slot home.
And that proved enough to secure all three points, with Will Norris never really troubled against his former club.
