Elan Evans made it eight goals in four games for Caernarfon this season with a hat-trick at Lon Isallt on Sunday.
The 17-year-old has now netted 23 goals in 24 first-team appearances since making her senior debut at the start of 2024-25.
While Caernarfon were good value for their first win of the campaign, the game was closer than the final scoreline suggests with Bay battling to the end.
Both teams started well, playing good passing football from defence to attack, but it was Caernarfon who broke the deadlock on six minutes through Ellie Morris-Dunn.
Trearddur Bay were still making nice openings, but could not find the key final pass.
Then on 12 minutes, new signing Jordan Roberts netted again for Town after a corner was not cleared.
The visitors made it three on 16 minutes when Morris-Dunn played a ball to Elan Evans, who bagged her first.
With Bay pressing forward, Elin Murley took her chance well to make it 3-1 after tidy passing football from midfield to attack, Jess Woods supplying the assist from the right.
Caernarfon pushed again before half time and scored twice with goals from Manon Evans and Sioned Bohana.
The second half started very much like the first with attacking football from both teams, but an own goal from centre back Lauren Bate on 50 minutes made it 6-1.
Caernarfon built on their advantage with goals from Elan Evans on 51 and 61 to complete her hat-trick.
Bay winger Murley grabbed her second on 79 minutes and midfielder Freya Davies added another late on to bring some respectability to the scoreline for the island hosts.
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