Town hit top spot in the division thanks to Saturday's exciting 4-3 victory at Luton Town while Pompey are also in excellent form, hammering Hartlepool 4-0 at the weekend in front of another large Fratton Park crowd.
Ladbrokes make Portsmouth 4/1 to win League Two this season with the Cobblers slightly bigger at 9/2.
Oxford United remain the favourites, however, at 13/8 to be the division's top dogs.