Dane Scarlett bagged a brace as Pompey battled from behind to beat Peterborough at a packed Fratton Park.
They got off to a disastrous start, with a mistake at the back gifting Jack Marriott a goal for the visitors.
But Scarlett grabbed an equaliser before the break and was teed-up by debutant Josh Koroma for the winner.
Danny Cowley made a single change from the side that won at Port Vale in the last league outing a week earlier.
Connor Ogilvie missed out after becoming a father in the early hours of the morning and was replaced at left-back by fit-again skipper Clark Robertson.
It meant that deadline day loan signing Koroma had to be content with a spot among the substitutes.
Ben Thompson started for the visitors, but fellow former Pompey players Nathan Thompson and Dan Butler were both unavailable.
The hosts showed their early attacking intent and when Ronan Curtis was brought down, Marlon Pack curled the free-kick narrowly over.
But their opponents were gifted a goal moments later, when Michael Morrison was caught in possession by Jonson Clarke-Harris.
He advanced forward and unselfishly squared the ball for strike partner Marriott to slot past Josh Griffiths.
It might have got even worse for the Blues just moments later, with Clarke-Harris’ angled attempt having to be turned around the post by Griffiths.
But Cowley’s men were otherwise impressive in the first half and after spinning sharply on the edge of the box, Curtis fizzed a shot narrowly past the post.
Curtis and Owen Dale were finding plenty of joy on the wings and Peterborough were having to defend resolutely.
It was Dale who was next to go close with a low attempt that flashed narrowly wide, while a Scarlett effort was then deflected into the side netting.
There should have been a leveller on 33 minutes when Dale found Curtis in space at the back post, but the Republic of Ireland international could not find the target from just a few yards out.
It did not take much longer for the equaliser to arrive, though, as a superb Robertson cross was nodded home by SCARLETT for his third goal in as many games.
Peterborough had a chance just before the break following a poor Griffiths kick, but Marriott could not make a connection with Clarke-Harris’ cross.
Half Time: Pompey 1 Peterborough 1
The hosts took a while to get going after the break, lacking some of the attacking fluency that had been so evident in the first half.
But a monster Pack throw might have led to a second goal, with the ball not quite landing right for Sean Raggett to make a clean connection.
Cowley decided to freshen things up with a double switch on 66 minutes, as Reeco Hackett and Koroma replaced Dale and Curtis.
And the debutant soon grabbed an assist to help Pompey take the lead for the first time in the game.
He found SCARLETT inside the box and the on-loan Tottenham striker continued his goal spree by sliding a shot through Frankie Kent’s legs and into the net.
The teenager was withdrawn alongside Tom Lowery on 76 minutes, with Joe Pigott and Joe Morrell adding some fresh legs.
And Cowley decided to shore things up for the closing stages, by bringing on Jay Mingi for Colby Bishop.
Peterborough were not looking too threatening, though, and when a Ricky-Jade Jones delivery was only partially cleared, Jack Taylor blazed the loose ball over.
And Pompey saw out the closing stages with relative ease to continue their fine start to the league campaign.
Pompey (4-4-2): Griffiths; Rafferty, Morrison, Raggett, Robertson (c); Dale (Hackett 66), Pack, Lowery (Morrell 76), Curtis (Koroma 66); Scarlett (Pigott 76), Bishop (Mingi 82)
Goals: Scarlett 37, 70
Booked: Rafferty, Robertson
Subs not used: Oluwayemi, Jacobs
Peterborough (3-4-1-2): Bergström; Knight, Edwards, Kent; Ward, Fuchs, Taylor, Burrows (Jones 77); Thompson (Poku 71); Clarke-Harris, Marriott (Mason-Clark 79)
Goals: Marriott 5
Subs not used: Blackmore, Tomlinson, Kyprianou, Randall
Referee: Samuel Barrott
Attendance: 18,168 (802 away fans)