Chris Long scored twice as the Cobblers and new boss Jimmy Floyd Hasselbaink claimed their second Sky Bet League One in the space of three days, beating a determined Portsmouth side 3-1 at a wet and windy Sixfields.
Burnley loan man Long and Matt Crooks scored in the opening 32 minutes to put Town 2-0 up and on control, but Pompey raised their game in the second half.
Matt Kennedy fired the south coast side back into it in the 49th minute, and although they went on to create several more chances they could find no way past the Town defence or impressive goalkeeper Matt ingram.
Long added the third with 20 minutes remaining and although Town again had to withstand plenty of pressure, they held on to claim their second win of the campaign.
The win lifts the Cobblers, who were rock bottom and pointless on Saturday morning, out of the bottom four and up to 17th in league one.
The Cobblers named an unchanged team from the one that secured a 1-0 win over Doncaster Rovers at Sixfields, the club's first win of the season.
That meant a second start in the claret and white for George Smith, who again lined up in a wide left position, but Hasselbaink tinkered elsewhere, with Crooks this time playing on the right of midfield in a 4-4-2 formation, with Alex Revell and Long up top.
The rain was pouring down as the game started, and there was also a swirling wind which made things difficult for the players.
That led to a scrappy opening spell, and although the visitors probably settled into the game better, they failed to make any attacking headway, until Matt Kennedy tried his luck from 20 yards, but his curling right-foot shot was too high.
Moments later a dangerous inswinging free-kick from Matt Grimes somehow evaded everybody and drifted wide, but it was to matter not, as the Cobblers went ahead on 18 minutes with a quality goal.
Crooks played the ball into Shaun McWilliams, who slipped a pass through the flat Pompey defence, for Long to race on to, and with Luke McGree deciding to stay at home, the Burnley loan man slid a low shot past the Pompey goalkeeper and into the net.
The Cobblers were now beginning to grow in confidence, and although they suffered a setback on 26 minutes when the excellent McWilliams was forced off with a foot injury after he kicked the bottom of a high Pompey boot, they extended their lead on 32 minutes.
Grimes again whipped an inswinging free-kick, and this time Crooks got his head on to it and the ball flew in to the net, via Pompey defender Matt Clarke.
Portsmouth were stung into action and almost reduced the arrears on 38 minutes as Ash Taylor stooped low to try and head clear a dangerous Jamal Lowe cross, and only succeeded in heading the ball against his own post.
Luckily for Taylor and the Cobblers, the ball then bounced to safety.
Portsmouth went even closer to reducing the arrears in the sixth minute of seven minutes of time added on, but Matt Ingram in the Cobblers goal produced an excellent finger-tip save high to his right to divert Stuart O'Keefe's dipping 25-yard effort over the bar.
The weather conditions worsened during the break, with the rain whipping in on a strong wind from the south west corner of the ground.
Pompey started the second half well and were back in the game on 49 minutes.
Kasim and Buchanan both failed to properly clear the danger when they had the chance, the ball fell invitingly to Kennedy just insides the area and he drilled it home to make it 2-1.
Roared on by their large contingent of supporters in the south stand they were attacking, Pompey were suddenly the dominant force, and they twice went close to equalising through Nathan Thompson and Lowe, who was a whisker wide with a shot that flashed across goal.
To their credit, the Cobblers began to stem the blue tide and find their way back into the game.
They started to make some attacking inroads again, and on 70 minutes they increased their lead, with Long grabbing his second.
Brendan Moloney swung a deep cross in from the right wing, and as Revell challenged for the ball with Christan Burgess and Clarke they all missed it.
It landed at the feet of Long at the far post and he steadied himself before thrashing it past McGee and into the net to make it 3-1.
Pompey weren't going to lie down though, and they again applied plenty of pressure and shots, but there always seemed to be a Cobblers leg there to make the block.
On 84 minutes Damian McCrory's cross found Burgess at the far post, but his low header was kept out by Ingram.
The Town goalkeeper Ingram then had to be alert to keep out a couple of Stuart O'Keefe long-range efforts, but there was to be no fightback from Pompey, and Town could celebrate a second Sixfields win in the space of just three days.
Cobblers: Ingram, Taylor, Moloney, Pierre, Buchanan, McWilliams (30m, Kasim), Grimes, Long, Crooks, Smith (56m, Powell), Revell (77m, Richards). Subs not used: Cornell, Barnett, Waters, Poole
Pompey: McGee, Thompson, Clarke, Burgess, McRory, May (58m, Closse), O'Keefe, Lowe, Pitman, Kennedy, Chaplin. Pompey subs: Main, Donohue, Naismith, Bennett, Talbot, Bass
Referee: Darren Drysdale
Goals: 1-0 Long, 18 mins; 2-0 Crooks, 32 mins; 2-1, Kennedy, 49 mins; 3-1 Long, 70 mins.
Pompey fans: 1,153