View the photo gallery from the Blues' victory at London Road
Pompey netted twice in the second half to beat Peterborough 2-1 and climb into top spot in the League One standings.
Oli Hawkins opened his account for the season by heading home a cross from Ronan Curtis.
And it was Curtis who also provided the assist for Jamal Lowe to extend the visitors' advantage further.
Matt Godden reduced the Posh's deficit in stoppage-time, but the Blues held on to leapfrog their opponents in the table.