Matt Tubbs grabbed the only goal as Pompey maintained their excellent away record with victory at bottom club Newport.
The winner arrived in first half stoppage-time after the visitors had dominated without creating many clear-cut chances.
The game’s other big talking point was a change of officials after referee James Adcock was forced off injured.
Paul Cook made two changes from the side that won at Cambridge the previous week.
Adam Webster and Kal Naismith both made their first league starts of the season, with Matt Clarke dropping to the bench and Gareth Evans starting a three-match ban.
Also among the substitutes were recent loan signing Caolan Lavery, utility man Rommy Boco and fit-again goalkeeper Brian Murphy.
Pompey made a bright start and Gary Roberts sent a fine ball across the face of goal that none of his team-mates could make a connection with.
At the other end, Webster did well to turn behind Zak Ansah’s low cross and Aaron McCarey punched clear from the resulting corner.
But the Blues soon started to dominate possession and enjoy their usual patient passing game.
Kyle Bennett created a great chance on 17 minutes when he bamboozled his man down the left and sent a delivery into the box, but Roberts’ effort was blocked by Scot Bennett.
Roberts had another chance after Pompey advanced down the middle moments later, with his chipped effort flying wide.
The home support were growing frustrated by their side’s inability to keep hold of the ball, but Newport were not really being put under too much pressure.
And Lenell John-Lewis had the ball in the back of Pompey’s net on 31 minutes, only for the goal to be disallowed for a foul on Christian Burgess in the build-up.
There was then a lengthy stoppage as Adcock limped to the sidelines and had to be replaced by fourth official Wayne Barratt.
That drew comical – and somewhat uncaring – chants of ‘You’re Not Fit To Referee’ from the amused spectators.
It led to four minutes of stoppage-time and Pompey managed to forge ahead in the second of them.
Bennett sent a fine threaded pass through to TUBBS, who clinically slotted the ball into the bottom corner to send the large travelling contingent wild with delight.
Newport C0unty 0
The first action of the second half – once a qualified referee from the crowd had been sourced to take over fourth official duties – saw Scott Barrow booked for a late challenge on Tubbs.
It was a scrappy first few minutes, although both sides had the chance to score within a few seconds of each other on 53 minutes.
When Naismith won a free-kick on the edge of the box, Bennett quickly played it to Roberts, whose fierce drive was blocked.
Newport then broke quickly up the other end of the pitch and the moved ended with Mark Byrne firing inches past the post.
The hosts had another opportunity when Adam Barton conceded a free-kick in a dangerous position, but Tommy O’Sullivan’s curling effort was comfortable for McCarey.
Cook decided the time was right for a change just before the hour mark and Naismith made way for debutant Rommy Boco.
Pompey were struggling to find any fluency, although Bennett did see a long-range drive sail narrowly wide.
Another substitution followed on 68 minutes as Danny Hollands replaced Barton in the centre of midfield.
And the Blues had a great chance to wrap the points up soon after following a great move down the left involving Bennett and Enda Stevens.
County keeper Joe Day managed to get a hand to the latter’s low cross and the ball was agonisingly out of reach for either Tubbs or Roberts to poke home.
Pompey’s final change came on 75 minutes and saw Lavery come on for his debut in place of goalscorer Tubbs.
And the closing stages passed by pretty much incident-free as the Blues secured another three-point haul on the road.
Newport (3-5-2): Day; Partridge, Bennett, Donacien; Barnum-Bobb, O’Sullivan, Byrne (c), Elito, Barrow (Rodman 65); John-Lewis (Collins 65), Ansah (Boden 59)
Subs not used: Taylor, Holmes, Taylor, Klukowski
Pompey (4-2-3-1): McCarey; Davies, Burgess, Webster, Stevens; Doyle (c), Barton (Hollands 68); Naismith (Boco 59), Roberts, Bennett; Tubbs (Lavery 75)
Goals: Tubbs 45+2
Subs not used: Murphy, Clarke, Atangana, Chaplin
Referee: James Adcock (Wayne Barratt 40)