County fell to defeat in our second EFL Trophy game of the season, despite Will Evans' late goal.
Two goals in the space of 10 minutes from Ben Stevenson and Bryan Fiabema put FGR 2-0 up before Evans netted in second-half stoppage time.
Forest Green started on the front foot, as Regan Hendry's attempt after barely a minute was deflected wide for a corner that saw a header come off the foot of the left post before County cleared their lines.
Chelsea loanee Bryan Fiabema was the next to try his luck for Rovers but his strike from the edge of the box was straight at Joe Day and saved with ease.
Will Evans had a flicked attempt from just inside the area deflect over the bar before Fiabema became the second FGR man to fire a shot straight at Day from the edge of the area.
Reece Brown would then see a pair of shots go wide before the first half that finished without a goal came to a close.
FGR would have the first chance of the second half too, with Day needing to make a good save to push behind Fiabema's effort from a tight angle on the left of the box.
Day would need to be on top form 10 minutes into the second period, as he first clawed away a looping cross from Corey O'Keefe.
He then somehow managed to prevent Hendry on the rebound whose shot was saved by Day's feet but looped over the keeper, seeming certain to go in, but Day did brilliantly to grab the ball just before it crossed the line.
County came so close to opening the scoring in memorable style, however. A long throw from the right was only cleared as far as Robbie Willmott who steadied himself before unleashing a half-volley from 25 yards that whizzed narrowly wide of the left post.
It was Forest Green that took the lead in an impressive manner though as Stevenson found the back of the net on 69 minutes from a fair distance with a curling shot that beat Day and nestled into the bottom right corner for 0-1.
County almost levelled matters in the 73rd minute, but Omar Bogle headed Willmott's corner from the left narrowly wide.
It really should have been 1-1 14 minutes from time, but Nathan Moriah-Welsh rattled the crossbar after lovely work in the build-up play from Lewis Collins and Evans, with the latter backheeling into the path of Moriah-Welsh.
County were punished shortly after as Fiabema slammed home in the 79th minute as FGR seized on a loose pass before setting up the Norweigian forward for a powerful finish past day.
Newport did have something to cheer in second-half stoppage time though as Evans pounced on a loose ball to finish from a few yards to make it 1-2 late on.
Newport County: Joe Day, Cameron Norman, James Clarke, Declan Drysdale, Aaron Lewis, Robbie Willmott, Matt Dolan (C), Sam Bowen (Nathan Moriah-Welsh '63), Will Evans, Thierry Nevers (Lewis Collins '57), Chanka Zimba (Omar Bogle '63)
Subs not used: Nick Townsend, Adam Lewis, Scot Bennett, James Waite
Forest Green Rovers: Lewis Thomas, Corey O'Keefe, Oliver Casey, Ben Stevenson, Regan Hendry (C) (Sean O'Brien '81), Jacob Jones, Kyle McAllister (Myles Peart-Harris '67), Bryan Fiabema, David Davis (Finley Bell '88), Harvey Bunker, Reece Brown
Subs not used: Luke McGee, Dom Bernard, Jordan Moore-Taylor