Despite a late surge and dominant set-piece, the home side ran out of time to find an equaliser in a match defined by defensive resilience and refereeing frustrations.
The opening stages were a physical tug-of-war. While both sides displayed plenty of fight, the attacking structure remained elusive for much of the first half.
Edinburgh’s 10-12 axis of Nicole Marlow and Hannah Ramsay provided the spark.
Ramsay gave the hosts significant go-forward in the centre channels, while Marlow’s tactical kicking at fly-half kept the visitors under constant pressure.
The big story of the half, however, was the scrum. Edinburgh enjoyed full scrum dominance, but their superiority went largely unrewarded by referee Chelsea Gillespie – a theme that would frustrate the home crowd throughout the 80 minutes.
Against the run of play, Brython broke the deadlock on 27 minutes. Following an attacking scrum just 5m from the Edinburgh line, the Thunder forwards peppered the whitewash before Stella Orin wrestled her way over. Ffion Williams added the extras to make it 0-7.
The second period remained a stalemate until a disciplinary lapse shifted the momentum. Replacement Charlotte Russell was shown a yellow card for a dangerous tackle, leaving Edinburgh to defend a one-score deficit with 14 players.
The visitors were ruthless, capitalising on the numerical advantage almost immediately.
Seren Singleton crossed the whitewash with just 10 minutes remaining. With the conversion successful, the scoreboard read 0-14, leaving the hosts a mountain to climb.
To their credit, Edinburgh hit back instantly. After being held up over the line in a desperate goal-line stand, they worked the ball back into the Brython 22.
The breakthrough finally came through the backs: Marlow drew the cover defence perfectly before popping a pass to Hannah Walker in the wide channel.
The captain showed a blistering turn of pace to round her opposite number and dive over. Marlow nailed a pressure conversion to bring it to 7-14.
With the Hive Stadium crowd in full voice, Edinburgh hunted for a second score to snatch a draw.
However, the Thunder played the closing minutes with composure, milking the clock through a series of reset scrums to stifle the game and secure the victory.