RGC won an eight-try thriller thanks to the reliable boot of star fly-half Billy McBryde.
The North Walians took an early lead when an error by Nathan Trowbridge let in Tom Hughes as he chased down a kick.
The lead was doubled when Efan Jones broke loose in midfield and left the Swansea defence behind as he sprinted home to score.
Owen Morgan popped up in midfield to power over for a try for the home side but the North Walians responded immediately when Rhys Williams chipped into space, with the bounce favouring Sam Jones, who scored in the corner.
Swansea were soon on the front foot and a ...