Llanelli delivered a battling performance in North Wales, but a strong second-half display saw RGC claim the spoils 25-12 in Colwyn Bay.
It was the hosts who opened the scoring when flanker Dan Owen charged down a Josh Phillips kick to touch down. Sam Rogers converted.
Llanelli responded with a 25th-minute try from centre Corey Baldwin, who together with fellow Scarlet Eddie James, caused the hosts plenty of problems. Phillips converted to level the scores.
A Rogers penalty put RGC back in front, but the home side were reduced to 14 men midway through the half after prop Jordan Scott was shown red for throwing a punch.
Llanelli, who looked to play with plenty of adventure, made the most of the numerical advantage with scrum-half Luke Davies crossing for try number two. Phillips’s conversion saw the West Walians turn around 12-10 to the good.
However, Llanelli were unable to build on that lead in the second period.
Despite being a man down, RGC applied the pressure and with their set-piece a real threat, hooker Rhodri King touched down from a drive to regain the lead.
It needed some desperate home defence to keep Llanelli at bay, then the visitors found themselves down to 14 men with the yellow-carding of Iwan Shenton.
Dion Jones extended his side’s lead with a penalty and the game was sealed when RGC were awarded a late penalty try from a powerful scrum drive.