They had forged a 13-point lead but were forced into a desperate rear-guard action as the Wayne Proctor coached Quins threw everything at them.
“It was such a tough game,” said former Bridgend and Caerphilly prop Thomas.
“Without doubt, it was the two best youth teams in Wales going at it hammer and tongs and we’re absolutely delighted to have won the cup for we were hanging on at the end.
“I said, before the match, if we performed to our best, we would be tough to beat. We didn’t perform to our best but it was enough to win.
“Credit to Carmarthen, they ran everything. They came with a plan and threw everything at us but our defence held firm – I was proud of it.
“I thought the try we scored early in the second half was crucial. And, when we haven’t got the ball, we try to be a bit more busy.”
Tondu captain and hooker Ellis Major, who led from the front with an all-action display, said: “We started really well but Carmarthen Quins looked sharper when they had the ball.”
Generously, he added: “They were probably the better side. But we have worked hard on our defence and it paid off.”
