Dane Scarlett bagged a brace as Pompey battled from behind to beat Peterborough in packed Fratton Park.
They got off to a disastrous start, with an error at the back giving Jack Marriott a goal for the visitors.
But Scarlett equalized before the break and was groomed by debutant Josh Koroma for the winner.
Danny Cowley made just one 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 in-form skipper Clark Robertson.
That meant deadline-day loan signing Koroma had to settle for a place among the substitutes.
Ben Thompson started for the visitors, but fellow former Pompey players Nathan Thompson and Dan Butler were unavailable.
The hosts showed their intention to attack early on and when Ronan Curtis was knocked down, Marlon Pack curled in the free-kick narrowly.
But their opponents were gifted a goal moments later when Michael Morrison was taken in possession by Jonson Clarke-Harris.
He stepped forward and generously squared the ball for attacking partner Marriott past Josh Griffiths.
It could have gotten worse for the Blues moments later, with Clarke-Harris’ oblique attempt having to be returned 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 fired a shot just past the post.
Curtis and Owen Dale found great joy on the wings and Peterborough had to defend resolutely.
It was Dale who was next to close with a low attempt that narrowly blinked, while an effort from Scarlett was then deflected into the side netting.
There should have been a 33rd-minute equalizer when Dale found Curtis in space at the far post, but the Republic of Ireland international couldn’t find the target just yards away.
It didn’t take much longer for the equalizer to arrive, as a superb cross from Robertson was sent home by SCARLETT for his third goal in as many games.
Peterborough had a chance just before the break following a poor kick from Griffiths, but Marriott could not link up with Clarke-Harris’ cross.
Half time: Pompey 1 Peterborough 1
The hosts were slow to get going after the break, lacking the attacking fluidity that had been so evident in the first half.
But a monster throw from the Pack could have led to a second goal, with the ball not quite landing properly for Sean Raggett to make a clean connection.
Cowley decided to freshen things up with a double switch in the 66th minute, as Reeco Hackett and Koroma replaced Dale and Curtis.
And the debutant quickly landed 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 scoring streak by slipping a shot between Frankie Kent’s legs and into the net.
The teenager was taken off alongside Tom Lowery in the 76th minute, with Joe Pigott and Joe Morrell adding fresh legs.
And Cowley decided to consolidate things for the final stages, bringing in Jay Mingi for Colby Bishop.
Peterborough didn’t look too threatening, however, and when a Ricky-Jade Jones delivery was only partially obliterated, Jack Taylor kicked the stray ball.
And Pompey saw the final stages with relative ease to continue his strong 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
Reserve: Rafferty, Robertson
Unused subtitles: Oluwayemi, Jacobs
Peterborough (3-4-1-2): Bergstrom; Knight, Edwards, Kent; Ward, Fuchs, Taylor, Burrows (Jones 77); Thompson (Poku 71); Clarke-Harris, Marriott (Mason-Clark 79)
Goals: Marriot 5
Unused subtitles: Blackmore, Tomlinson, Kyprianou, Randall
Arbitrator: Samuel Barrot
Presence: 18,168 (802 away fans)
Pompey 2 Peterborough 1