Wales, who had beaten France in a thriller at Llandovery in their opening game, had to withstand a powerful second-half comeback from the old enemy after leading 8-0 at half-time.
But despite being reduced to 14 men in the closing exchanges, Wales held their nerve with skipper Calum Thomas and outstanding No. 8 Reuben Tucker to the fore.
After a lively start from both sides it was Wales who struck first in the 12th minute through the razor-sharp Treharne.
A barnstorming run from prop Darren Harries took play to the shadow of the English posts and with the ball recycled quickly a clever miss-out pass found the Scarlets full-back who stepped inside the cover to dive over.
Fly-half Lewis Williams, who was controlling matters astutely, pushed the conversion wide, but extended Wales's lead on 20 minutes with a smart drop-goal.
Williams almost produced a superb solo score, chipping over the English defence and hacking on, but England right wing Jack Masters got back just in time to deny the No. 10.
Wales finished the half strongly with skipper Thomas providing a stream of quality line-out ball from the tail and scrum-half Lewis Jones proving a constant livewire behind a pumped-up set of forwards.
However, some desperate English cover denied flying Welsh wing Harry Robinson and the home side had to be satisfied with an 8-0 lead at the break.
Wales started the second period as they had left off the first, on the offensive with prop Harris and centre Cieran Driscoll both testing the English cover.
But with indiscipline creeping into Welsh ranks it was the visitors who reduced the arrears with a brace of penalties from centre Tommy Bell - the second after a blistering counter-attack from full-back Charlie Walker.
With England's forwards starting to dominate, Bell came close to giving his side the lead with a long-range attempt from halfway.
Wales's replacement scrum-half Jean-Baptiste Bruzulier was then sin-binned with six minutes remaining, setting up a tense finale.
But fly-half Williams again kept his nerve with a superb 40-metre penalty in stoppage time to secure the win.
Wales now move onto Cardiff RFC on Wednesday, April 15, where they will play Italy Under-17s, who lost 59-8 to France Under-17s yesterday.
France's tries were scored by centre Jonathan Danty, wings Yohan Artru and Quentin Genest (two), replacement Emanuel Husquin (two), full-back Maxime Payen and fly-half Ilian Perraux (two), who also kicked five conversions. Scrum-half Etienne Quiniou also landed two conversions.
Italy's points came via a try by replacement Filippo Guiratti and penalty by fly-half Carlo Canna.
Tries: L. Treharne Pens: L. Williams D-g: L. Williams
L. Treharne (St Michael's Llanelli; Scarlets); G. Hunter (Lampeter CS; Scarlets), C. Driscoll (St Cyres CS; Blues), T. Pascoe (Cardinal Newman RC; Blues), H. Robinson (Radyr CS; Blues); L. Williams (Tonyrefail CS; Blues), L. Jones (Ysgol Garth Olwg; Blues; repl J-B. Bruzulier (Whitchurch HS; Blues) 55); D. Harries (Brecon HS; Blues), J. Elley (Hawthorn HS; Blues), S. Lee (Coedcae CS; Scarlets; repl T. Jones (Aberdare Boys; Blues) 49), J. Gardiner (Ysgol Gyfun Bro Myrddin; Scarlets), J. Jones (Ysgol Gyfun Ystalyfera; Ospreys), E. Jenkins (Bryn Celynog CS; Blues; repl R. Bloomfield QEHS Carm; Scarlets 70), R. Tucker (Cowbridge CS; Blues), C. Thomas (Tonyrefail CS; Blues, capt)
Pens: T. Bell (2)
C. Walker; J. Masters, E. Daly, T. Bell. M. Jennings; E. Hainsworth, O. Massey-Birch; L. Cowan-Dickie, W. Tanner, N. Morris (repl K. Sinkler 58), J. Robinson, D. Barrow (capt), J. Watkins, A. Stout, M. Hawkin.