Second-half goals from Josh Davison and an Aaron Collins’ penalty pushed 10-man Forest Green back into the play-offs.
A lethargic first-half, devoid of chances, only brought about a free header for Tranmere’s Peter Clarke and a scuffed volley for Forest Green’s Scott Wagstaff.
Collins picked up a stoppage-time yellow for simulation on the edge of the box when taking a dive under a challenge from Manny Monthe.
Forest Green nudged ahead on 50 minutes – Davison with a sumptuous finish beyond Joe Murphy after the ball dropped to him from a Kane Wilson cross.
Seven minutes later, Ebou Adams was handed a second yellow after an aerial challenge on Calum MacDonald.
Forest Green made it 2-0 with nine minutes to go – Collins converting the penalty he won himself after Murphy upended him in the box.
Deep into six minutes of injury time, a thumping Kieron Morris strike handed Tranmere late consolation.
Forest Green move up to seventh and travel to Oldham on the final day, while Tranmere remain in the play-offs but dropped to sixth.