Pompey battled from behind to secure an ultimately comfortable victory over Peterborough at Fratton Park.
John Mousinho's men fell behind when Ricky-Jade Jones bent a shot into the net midway through the first half, but Colby Bishop and Abu Kamara both struck to turn things around.
And the Blues made their dominance count after the break, when Kamara flashed the ball across the face of goal and Regan Poole turned it into the net.
Joe Morrell was sent off for a second bookable offence late on, but the hosts held on with relative ease to secure a 3-1 win and maintain their unbeaten start to the League One campaign.