Sean Raggett was on target as Pompey returned to winning ways in their first ever meeting with Forest Green.
The defender headed home during a first half that was largely comfortable for the Blues at The New Lawn.
But their opponents put up more of a fight after the break and applied some pressure, without really troubling Josh Griffiths.
Danny Cowley made five changes from the side that were beaten at Charlton on Monday evening.
Zak Swanson and Jay Mingi were both handed their first league starts, while there were returns for Ryan Tunnicliffe, Ronan Curtis and Joe Pigott.
Michael Morrison, Joe Morrell, Josh Koroma and Dane Scarlett all dropped to the bench, while Marlon Pack served his one-match ban.
Former Blues keeper Luke McGee was between the sticks for the hosts, who have title-winning skipper Michael Doyle serving as assistant head coach.
The visitors quickly took control of the contest, with the excellent Mingi running the show in the middle of the pitch.
And the deadlock was almost broken on nine minutes, when he combined with Curtis to find Colby Bishop in the box.
The striker’s shot was diverted against the crossbar by McGee and Pigott could not head on target from the resulting corner.
But the Blues did go ahead soon after, with Owen Dale delivering a free-kick from wide on the left and RAGGETT making sure he got there first to head home.
Despite not being put under too much pressure, Pompey were struggling to force McGee into more action.
A Dale free-kick was claimed underneath the bar by the keeper, while a couple of dangerous Curtis cross were intercepted.
Then, after a deep Tunnicliffe cross had caused a scramble inside the area, Pigott rolled a shot past the post.
Griffiths was having a quiet afternoon at the other end and was certainly not troubled by an Armani Little effort that flew high over the bar.
It was Pompey who had the final say just before the interval, with Curtis curling a shot wide after more good work from the impressive Mingi.
Half Time: Forest Green 0 Pompey 1
Rovers were quicker out of the blocks when the action restarted, but still could not find their shooting boots.
One passage of passing play ended with Myles Peart-Harris hitting the roof of the stand, while another led to Harry Boyes’ cross being claimed by Griffiths.
Pompey had not really got going and Cowley freshened things up just before the hour mark by bringing on Scarlett for Pigott.
Their opponents then threatened an equaliser when Corey O’Keeffe’s cross drifted towards the net and had to be palmed away by Griffiths.
Two more changes quickly followed for the visitors, as Koroma and Reeco Hackett replaced Dale and Curtis out wide.
Forest Green were still looking dangerous, though, and after some sustained pressure, Little flashed a shot wide.
Hackett was looking lively following his introduction and swapped passes with Tunnicliffe before finding Koroma, who spun and fired narrowly off target.
And Hackett had a chance of his own on 78 minutes, cutting in from the right and hitting a left-foot curler that had to be beaten away by McGee.
The points should have been wrapped up moments later, but Scarlett nodded wide from close range after Swanson had sent in a fine cross.
Mingi’s afternoon then came to an end, with the midfielder appearing to cramp up and limping off to be replaced by Morrison.
Six minutes of added time saw some nerves among the travelling fans, although they almost vanished when Scarlett’s neat touch provided an opening.
But both he and Bishop seemed to go for the shot at the same time and McGee kept it out with his leg.
McGee sensed he could be the hero by going up for a Forest Green corner right at the death, but Pompey dealt with it and the final whistle immediately followed.
Forest Green (3-4-1-2): McGee; Bunker, Marques, Cargill (c); O’Keeffe, Hendry (March 62), Stevenson, Boyes (Fiabema 87); Peart-Harris; Little (McAllister 74), Wickham (Matt 74)
Booked: Hendry, Little, Cargill
Subs not used: Thomas, Casey, Bernard
Pompey (4-4-2): Griffiths; Swanson, Raggett, Robertson (c), Ogilvie; Dale (Hackett 62), Tunnicliffe, Mingi (Morrison 81), Curtis (Koroma 62); Pigott (Scarlett 58), Bishop
Goals: Raggett 17
Booked: Tunnicliffe, Scarlett
Subs not used: Oluwayemi, Hume, Morrell
Referee: Will Finnie
Attendance: 4,011 (1,195 Pompey fans)