Ryan Watson scored two in two minutes to continue his sensational form while Fraser Horsfall's close-range header and a fourth by Sam Hoskins - or Ryan Edmondson - put the gloss on a highly impressive victory. Here are our player ratings from the PTS....
5. Joseph Mills
An early dart by Harness was ominous but from that moment on Pompey's danger man was kept very quiet by Town's skipper. Replaced by Harriman late on as a precaution... 8
6. Jack Sowerby
Didn't have a big role to play in possession but his hard graft in midfield offered good protection to the defence and ensured little got through to the centre-backs. Portsmouth rarely looked capable of breaking down the hosts... 7.5
7. Shaun McWilliams
Gave his midfield counterparts the runaround with a typically combative, industrious, hard-running midfield showing. Kept things simple but effective in possession, with his hooked balls over Pompey's defence causing plenty of problems... 8.5
8. Ryan Watson
His spectacular form in front of goal continued with two in three minutes which set Cobblers on their way. The first was a magnificent free-kick, the second a towering header. Got through plenty of work off the ball too. Outstanding again... 9