Pompey showed they can perform at home as well as on the road by dismantling Northampton at Fratton Park.
John Marquis continued his fine run of goalscoring form by breaking the deadlock late in the first half.
And the Blues survived a scare immediately after the interval to double their advantage through the same player.
Ronan Curtis – recalled to the side – then raced clear to curl home a third goal and end the match as a contest.
But there was still time for Marcus Harness to head home his seventh of the season in the closing stages.
Kenny Jackett made one change from the side that impressively dismantled Sunderland at the weekend.
Michael Jacobs injured his knee at the Stadium of Light, so Republic of Ireland international Curtis replaced him wide on the left.
The game began at a frantic pace, with the action constantly switching from one end of the pitch to the other.
But both sides were lacking that all-important killer pass, with attacking moves often breaking down in the final third.
Northampton should have broken the deadlock on 16 minutes after some great work by Ryan Watson.
But after skipping past a couple of challenges with graceful ease, the forward undid his good work by screwing horribly wide.
Pompey then had their first decent opportunity, breaking quickly through Andy Cannon, Harness and Curtis, with Marquis’ angled effort deflected behind.
Neither keeper was being given too much to keep them warm on a chilly south coast evening, though.
But when Jonathan Mitchell was called into action on 39 minutes, he could not prevent the hosts taking the lead.
The stopper was only able to parry Ryan Williams’ low curling effort straight out in front of him, with the ball hitting MARQUIS and taking a slight deflection off Cian Bolger on its way into the net.
And the advantage was almost doubled just a few moments later, with Marquis not getting enough on his shot after being played through by the dangerous Harness.
Pompey were definitely finishing the half on top and when Cannon tried to launch a break, he was pulled back by scruff of the neck by Bolger.
It was as blatant a foul as you could possible see, with referee Trevor Kettle brandishing his first yellow card of the evening.
Northampton Town 0
The second half was not even two minutes old when the Cobblers were handed an excellent chance to level.
A heavy touch from Sean Raggett let in Sam Hoskins and the visitors felt he was fouled by the defender.
But the ball ran free for Ricky Korboa and when his shot was beaten away by Craig MacGillivray, the follow-up from Watson had to be headed away by a well-placed Jack Whatmough.
And Pompey made them pay for their profligacy by scoring twice in quick succession to gain a commanding lead.
Callum Johnson got free down the right and picked out Curtis, whose header was finely saved by Mitchell, only for MARQUIS to bundle the ball over the line.
It soon got even better for the Blues, as CURTIS was given time to advance forward and bend a shot into the bottom corner.
The visitors tried to hit back and a free-kick from debutant Alan Sheehan was brilliantly repelled by an athletic MacGillivray stop.
Both sides looked capable of adding to the scoring, although the action did calm down a bit as the half progressed.
Pompey looked to shore things up, with Harness going out to the right and Williams tucking in behind Marquis.
And the lively Harness was next to go close, cutting in from the flank and dragging narrowly past the post.
But HARNESS did have the goal his performance deserved late on, stooping to nod into the net when Cannon lifted the ball into the centre from the by-line.
Sam Hoskins sent a shot dipping over the bar as Northampton sought a consolation, but the Blues were able to add a clean sheet to their fine attacking display.
Pompey (4-4-2): MacGillivray; Johnson, Whatmough, Raggett, Brown; Williams (Morris 90+2), Naylor (c), Cannon (Close 90), Curtis; Marquis, Harness
Goals: Marquis 39, 47, Curtis 50, Harness 83
Booked: Williams, Harness
Subs not used: Bass, Mnoga, Nicolaisen, Pring, Hiwula
Northampton (3-4-3): Mitchell; Bolger (c), Sheehan (Martin 78), Horsfall; Hoskins, Sowerby, Missilou (Rose 58), Harriman; Watson, Smith, Korboa (Chukwuemeka 66)
Subs not used: Arnold, Racic, Adams, Marshall
Referee: Trevor Kettle