Following comprehensive wins at Gillingham and Sunderland, the Blues are tasked with continuing their fine progress following an indifferent start to the season.
Kenny Jackett will be forced into making one change to his starting line-up, with Michael Jacobs ruled out injured for up to six weeks.
But will the Pompey boss opt to make any other adjustments to his side? Take a look at how we think the Blues will start and who will be on the bench below.
1. Goalkeeper - Craig MacGillivray
Dominated his area at Sunderland and will be aiming for a fourth league clean sheet of the season. Photo: Daniel Chesterton
2. Right-back - Callum Johnson
Starting to really find his feet following his summer move. Quick throw yielded the opener at Sunderland and was unlucky not to get an assist when John Marquis was offside. Photo: Joe Pepler
3. Centre-back - Jack Whatmough
Been in imperious form this season and will be given another physical challenge against Northampton. Photo: Joe Pepler
4. Centre-back - Sean Raggett
Formed a great understanding with Jack Whatmough and looks set to continue keeping Rasmus Nicolaisen out of the team. Photo: Joe Pepler