Pontypridd may have lost their coach and captain in recent weeks, Dale McIntosh and Chris Dicomidis both heading to the Cardiff Blues, but they still had too much for the Quins as Evans scored a try, two conversions and two penalties.
Prop James Howe added a brace of tries and the only response for the Quins was a penalty from fly half Craig Evans and a late consolation try by centre Rhys Williams. The victory means Pontypridd are now five points clear at the top of the table.
A late inclusion at fly half, Jarrod Evans gave the visitors an early 3-0 lead as Pontypridd dominated the opening exchanges.
Quins responded with a series of drives and outside half Craig Evans soon levelled things up with a penalty of his own. At 3-3, the game was a tight affair but it was Pontypridd who moved into the lead with Howe crossing for his first try of the day.
Winger Owen Williams gave the visitors field position with an incisive break and when Craig Locke found Howe in support, the prop steamed over. Jarrod Evans converted and added a second penalty right on the half time whistle for an interval advantage of 13-3.
Both sides gave it everything at the start of the second half, with Carmarthen flanker Will Boyde yellow carded for infringing at a ruck.
With a man advantage, Pontypridd knew they had to strike and they did just that as Jarrod Evans jinked his way to the line for a try he converted himself. Quins were now up against it as their perfect record looked under threat. And although they gave it everything in attack, they failed to break down a resolute Pontypridd defence.
Having endured a long period under the cosh, Pontypridd then struck a decisive blow, poaching line-out ball for lock Dicomidis, on his last appearance before joining the Blues, to gallop clear and find Howe in close support.
It proved to be a decisive score and although Williams hit back for Carmarthen after man of the match Owen Sheppeard was yellow carded for Pontypridd, it was not enough.
Carmarthen Quins: Tries: Williams; Pens: Evans.
Pontypridd: Tries: Howe (2), Evans; Convs: Evans (2); Pens: Evans (2).