The pace of East Wales' Aimee Williams put the visitors 0-2 up with two tries in the first 3 minutes, but Mererid Hughes and Rhiannon Sheen brought West Wales level before the break.
Consecutive efforts from Paige Portman (East) and Emily Lewis (West) maintained the balance and took the score to 3-3 within 7 minutes of the restart. West Wales' Cherish Watts put the home side ahead for the first time 20 minutes into the second half, but Rhiannon Gowen pulled East back shortly after.
With the score teetering in the balance, it was East that claimed the final winning points of the game, with Aimee Williams running in a superb individual try to take her hat-trick and a 4-5 win for the visitors.
West Wales dominated the U17 game, with outstanding performances from centre Adrianna Taviner and flanker Sioned Harries.
The latter opened the scoring within the first five minutes, claiming the first of her two tries of the game. Shortly after, full back Kerin Lake showed her exceptional pace with a blistering run down the wing, only to be brought down by a strong East defence just inside the 22.
The score read 12-0 at the break thanks to Harries' second try and Bethan Preece's neat conversion. Preece added a further five points midway through the second half to firmly secure a 17-0 victory for West Wales.