A stunning Ollie Banks strike gave Tranmere a slender lead after the first leg of a fiery League Two play-off semi-final with 10-man Forest Green.
Gavin Gunning was dismissed after 15 minutes for kicking out at Jay Harris.
Ten minutes later the hosts made the extra man count when Banks moved into space and smashed in a glorious 25-yard shot via the underside of the bar.
Tranmere’s top scorer James Norwood had four good chances to extend the lead but Forest Green held out.
Norwood could easily have been dismissed before Gunning saw red, the division’s leading marksman lucky to escape yellow cards for two rash challenges.
But he then went close to adding to the lead, first seeing a shot deflected just wide, then blazing wildly over from close range before shooting just off target from a right-wing cross.
The visitors, who won both league meetings this season, posed a threat on the break, notably when Christian Doidge dragged a first-half shot just wide.
Tranmere remained the more likely scorers with Norwood going close late on, but they were unable to add to their lead heading into the second leg in Gloucestershire on Monday.
The Merseyside club are bidding to return to League One for the first time since 2014, while Forest Green have never featured in the third tier.