The winger, who only took up rugby a year ago, went over in the corner with just under nine minutes remaining of a thriller that ebbed and flowed with the lead changing hands five times.
CRCC had an exciting attacker in full-back Mirain Jones and jackaling flanker in Mali Williams but Haverfordwest were a shade too strong.
Centres Ella Sturley and Megan Davies were a potent pairing with a knack of doing the right thing at the right time to produce a decisive contribution.
Haverfordwest were 10-8 behind at the end of the first half with CRCC scoring tries through replacement front-rower Beth Kenure and centre Laura Stewart.
Lock Jana Neumann had ploughed over for Haverfordwest with outside-half Elin Williams being successful with a penalty.
They took the lead six minutes into the second half when Sturley combined with Davies for the latter to score, Williams converting.
CRCC weren’t finished though with a quick tap-penalty from Jones culminating in left-wing Sophie Longland touching down in the corner with Helena Snuggs landing the conversion to put them back in front, 17-15.
But they failed to clear following the restart and defended heroically under incessant pressure from Haverfordwest. The dam eventually broke with Sturley exploiting an overlap for James to dive over for the winner.
Scorers
Haverfordwest – Tries: Jana Neumann, Megan Davies, Jess James; con: Elin Williams; pen; Williams.
CRCC – Tries: Beth Kennure, Laura Stewart, Sophie Langland; con: Helena Snuggs.
