PONTARDDULAIS lost 20-3 to division three west leaders Amman United after two tries in the last 15 minutes. It was 10-3 at half-time.
The scrummaging of the big Amman pack proved the difference despite a superb performance by Bont back-rower Jonathan Hire.
For Amman, fly-half Adrian Thomas dropped a goal, they were awarded a penalty try, converted by inside centre Rhys Thomas, flanker Sean Mangan powered over and replacement scrum-half Joel Foster also crossed.
Bont's neighbours Gorseinon, in fourth spot, were involved in a cracking game at home to fifth-placed Llanelli Wanderers, winning 44-38.
The Wanderers led 24-13 at half-time but a burst of scoring after the break took the hosts into the lead, though it still needed an interception try at the end to seal victory.
Gorseinon scored seven tries through prop Geraint James (3), wing Damian Rowe (2) and second rows Nicky Southgate and Ben Cross. Centre Andrew Steel landed three conversions and a penalty.
For the Wanderers, centre Rhydian Morgan got a hat-trick, and wing David Jenkins and fly-half Honny George also crossed. Full-back Nick Gale converted all five and put over a penalty.
Second-placed Newcastle Emlyn won 32-10 at home to Llandeilo, third-placed Tenby won 29-24 at Milford Haven, Tumble lost 33-15 at Cardigan and Pontyberem defeated visiting Lampeter 30-17.
The win takes Pontyberem up to third from bottom, four points clear of both Lampeter and Milford Haven.