Romulus were held to a frustrating draw by ten man Rainworth on Monday, letting a slender lead slip moments after finding their breakthrough.
Rainworth were reduced to ten men when Steve Kennedy saw red on 50 minutes for an off-the-ball elbow on Chris Morris.
It could have been significantly worse for the Wrens after defender Chris Timons kicked out at Roms midfielder Gavin Day in the first half, but he received just a yellow card from referee Mike Bingham.
Ben Spargo blazed over inside the first minute for Rainworth while Johnson cleared the crossbar for Romulus in a tepid start.
The home side's best chance of the opening half came eight minutes before the break, but Nathan Blissett's cross-shot didn't trouble Joe McCormack.
There ws little goal-mouth action until Johnson's struck, drilling home through a mass of bodies from 20 yards following Rob Evans' overlapping run down the right.
However, straight from the restart, Danny Bacon played Craig Mitchell through for Rainworth, who cut inside drawing a trip from Roms full back Todd Evans - Lynam blasted his spot-kick home with aplomb.
There was little further incident in the closing stages as the resolute visitors snuffed the game out efficiently.
ROMS: Exall, S Robinson (Ro Evans 54), T Evans, Richards-Everton, Male (c), Day, Morris, Walker, Blissett, Johnson, Reid (Price 84).
Unused subs: Lee, R Robinson.