A crowd of more than 500 turned up for a traditional and typically physical and bruising Welsh derby in the new home and away expanded Celtic Challenge.
Brython will host the return game against Gwalia in the second game of Welsh derbies to open the season at Parc y Scarlets next Saturday.
Fly-half Carys Hughes announced her return to Celtic Challenge with a personal haul of 17 points, including a try and six conversions. Gwalia crossed for six tries and Brython four tries.
The Gwalia pack and set-piece proved to much for Brython with Wales duo – scrum half Sian Jones and Number 8 Gwennan Hopkins – the pick of an impressive display by the home side.
There were Wales 12 Test stars selected in the starting line-up for both sides, with Gwalia the  more experienced side with eight Wales internationals, while Brython had four Wales stars in their starting line-up.
During a tense and physical opening both teams when scrum half Sian Jones launched an interception break to remind everyone why she was selected by Wales for the women’s Sin Nations and WXV campaigns.
But it was Brython who opened the scoring when hooker Chloe Gant crossed for a try from short-range. Ellie Tromans missed the conversion
Gwalia replied when openside flanker Paige Jones crashed over after a slick lineout to level the scored. Hughes slotted over the conversion to give Gwalia a 7-5 lead.
Gwennan Hopkins created another break and hooker Molly Reardon took advantage to launch herself at the Thunder defence, but the visitors defence held firm and survived an intense period of pressure.
The Lightning stretched their lead when Wales wing Catherine Richards latched on a stray Thunder pass and sped away and ran in from 40m for a well taken interception try to stretch the home side’s lead.
Hughes added the conversion to make it 14-5 before Thunder went down to 14 players when prop Katie Carr was shown a yellow card and Lightning tool full advantage and prop Maisie Davies crossed for the home side’s third try.
Hughes added her third conversion to stretch her side’s lead to 21-5 at half-time. After the break, the fly half scored her side’s fourth try and converted her own try to stretch Gwalia’s lead to 23 points.
Backrow Lily Terry crossed for a fifth try from short-range and Hughes added another conversion to make it 35-5 before Thunder replied with a try by replacement Evie Hill for the visitors second try of the afternoon.
With Gwalia down to 14 players due to a yellow card before captain Natalia John and wing Eleanor Hing crashed over for Brython’s third try to make the score 35-17.
Gwalia signed off with a sixth try by replacement Caitlin Lewis and fly-half Hughes added her sixth conversion.
Davies, who switched to the back row towards the end of the game, produced an outrageous show and go as Gwalia sealed an impressive victory.