But with two minutes remaining, the Carmarthen forwards drove for the line and remarkably, after a try-line pile up it was centre Alex Wilkins who came up with the ball for a try that levelled the scores at 25-25.
Craig Jones nervelessly added the conversion to seal a victory which sends Carmarthen two points clear at the top with only next weekend's visit of Narberth to come.
Tonmawr's fate is still in their own hands. However, having two games remaining, first away at Whitland next Saturday followed by another away trip to Waunarlwydd the following Wednesday, two wins would be enough.
In the East, leaders Caerphilly missed a golden opportunity to announce themselves as title favouries as they allowed second placed Pontypool to come back from 9-3 down to secure a priceless 12-12 draw.
Victory would have given Caerphilly a six point lead at the top but, with two games in hand and now sitting only two points behind the Cheesemen going into the final week of the season, Pooler are now firm favourites to finish top of the pile.