View the photos from the Blues' latest Fratton triumph
Pompey battled from behind to beat Northampton 3-1 in their final game of 2017.
Chris Long had given the Cobblers the lead, only for the hosts to hit back with a couple of goals in the space of four minutes at the end of the first half.
Matty Kennedy drilled a shot into the bottom corner to level, while Oli Hawkins then converted Christian Burgess' cross with a fine header.
Dion Donohue teed-up Hawkins for another goal after the interval and the Blues carved open several more decent chances.