The leaders took a while to get into their stride, then raced clear by scoring six tries with fly half Mark David gaining a try, five conversions and a penalty goal, while skipper Karl Hocking notched his 116th league try.
The Old Parish also ran in tries by flanker Marcus Sainsbury, wing Gareth John, centre Alun Brown and wing Gareth Holmes, while fly half and skipper Stuart Morris placed three penalty goals for the Athletic in a game well controlled by Clayton Thomas.
Glamorgan Wanderers remained in third place despite beating UWIC 36-12, but are now just one point behind Llangennech with a game still in hand and a better try-count.
No 8 Emyr Christopher had an outstanding game and he, Mark Heywood, Dave Willey, Lee Mullane and replacement scrum half Gareth Spain went over with Heywood converting one and landing two penalties and Jason Pocock also placed a penalty.
The students ran in tries by Rhys Edwards and Gareth Dacey and Phil Dolman converted one.
Blackwood battled their way to a 25- home win over Builth Wells and went out of therelgation zone, moving over Fleur de Lys, Carmarthen Athletic and UWIC in the process.
Fly half Jeremy Lloyd led the way with a penalty, drop goal and two conversions and tries came from Jamie Sims (2) and Christian Perry, while Rob Lloyd placed a lone penalty for Builth Wells.
Bonymaen jumped from seveth to fifth place after a 30-0 win over Tonmawr, who now are staring relegation in the face and have eight game to survive, but are already 13 points away from safety.
Scrum half Gareth James, formerly of Penygraig, notched four of the five tries by the Parc Mawr club and wing Chris Griffiths also crossed with Anthony Evans placing a penalty and conversion.
Warren Gatland and Sam Warburton look ahead to this week's crunch RBS 6 Nations tie against France, where the Wales skipper in particular is keen to make his mark, as Paris has proved a bleak place for him in the past.
Following their historic win over England, Wales Under 20 suffered a narrow, 36-34 loss to their Scottish counterparts last weekend, despite outscoring them by five tries to three. Watch the match highlights and reaction.
WRU TV go behind the scenes with the Wales squad as they put the final touches in place ahead of the clash against Scotland at Murrayfield. Follow the squad on their captain's run, the kickers visit to Murrayfield and Neil Jenkins' press conference