Swansea claimed the West Wales bragging rights thanks to a 34-23 victory in an entertaining Boxing Day derby at St Helen’s.
The All Whites turned a tight contest on its head midway through the second period to claim the bonus-point win in the third meeting between the clubs this season.
It was Llanelli who were first on the scoreboard through a penalty from fly-half Josh Phillips.
The visitors extended their advantage after nine minutes when wing Eddie James defused a dangerous Swansea attack by claiming an interception and showing good pace to race to the corner. Phillips was wide with the tricky conversion attempt.
Cai Evans reduced the advantage for the hosts with a couple of penalty successes, but Llanelli claimed a second try on 35 minutes when prop Ben Watson powered over from a strong line-out drive.
The scores, though, were level at 13-13 going in at the break thanks to a Swansea try from scrum-half Rhodri Lewis on the stroke of half time.
Fly-half Phillips added another penalty on the hour mark to put Llanelli back in front, but after wing Jack Price was yellow carded for a professional foul, the All Whites took a firm grip of the game.
Replacement hooker Garin Lloyd touched down on the back of a close-range line-out drive, then wing Iestyn Hopkins raced over for his side’s third of the afternoon.
Back-rower Harri Deaves added the bonu-point score with eight minutes remaining, with Llanelli claiming a consolation score in stoppage time courtesy of replacement No. 8 Nathan Hart, converted by fellow sub Tal Rees.
Llanelli return to Indigo Premiership action in front of the S4C cameras on Thursday, January 5 when they host Ebbw Vale at Parc y Scarlets.
Swansea – tries: R. Lewis, G. Lloyd, I. Hopkins, H. Deaves. Cons: C. Evans (4). Pens: Evans (2)
Llanelli – tries: E. James, B. Watson, N. Hart. Con: T. Rees. Pens: J. Phillips (2).