Both teams went into today's double header of fixtures unbeaten, knowing a win at Pandy Park would see them win the title.
And after the Ospreys had comfortably seen off the Dragons in the first game of the day, a four try salvo was enough to see the Scarlets to a 22-5 win.
Rhian McCulloch had exchanged tries with Megan Jones for the Blues as the two sides ended a tense, competitive first half level at 5-5. But three scores after the break from Rachel Norris, Abi Williams and Jasmin Joyce saw them move out of sight against a Blues side inspired by a superb individual performance from fly half Jones.
The eventual winners had started the game in bright fashion and were ahead when McCulloch finished superbly in the corner after showing a decent turn of pace to escape the Blues' defence.
Fly half Jodie Williams missed the conversion but was engaged in a ding-dong battle with opposite number Jones, the two players standing out impressively. And although they were behind, Jones was getting the Blues back into the game.
A period of sustained pressure saw the Blues pound the Scarlets' line though Abi Williams held the ball up in a piece of great defensive work.
The pressure eventually told though and it was no surprise to see the outstanding Jones dot down to get the Blues back into things.
That was the end of the scoring as a competitive first half ended 5-5.
With the title at stake, the start to the second period was understandably tense but it was the Scarlets who were doing the pressing. Second row Norris soon added a second try with Williams converting for a seven point lead.
The second half was then interrupted by a serious injury stoppage but the Blues were showing up well as they looked to reduce their deficit. Jones was at the heart of everything that was good for the girls in pink but sadly she could not break down the opposition defence.
And two late scores made sure of the Scarlets' triumph. First centre Williams broke clear to clinch the win before wing Joyce pounced on a kick through to add gloss to the scoreline.
Players who featured in today's games can next be seen in action on April 28 at Llandovery RFC. A finals day will see a west Wales U18 girls side take on one from east Wales.