Wales centre Jonathan Davies crossed for two tries to help put the Scarlets back in the RaboDirect Pro12 play-off places with an impressive derby win over Cardiff at Parc y Scarlets.
The Scarlets now need to beat Treviso next Friday night to secure that play-off place.
Davies' tries came in each half and the third score came from full-back Liam Williams, while the Blues could only manage two penalties from the boot of Leigh Halfpenny.
The Blues went into the lead on 18 minutes as Halfpenny found the target with his first penalty. A side-step and sprint through a gap saw Davies go behind the scrum for Williams to convert, while in the final five minutes of the half Halfpenny and Williams swapped penalties.
A good move from a scrum ended with Jonathan Davies bursting over from eight metres.And seven minutes later Liam Williams exploited a huge gap in midfield to go over for the third try converted by Priestland, who played the final 15 minutes.
Scorers – Scarlets: A Davies (2), L Williams tries; O Williams pen, 2 cons; Priestland con. Cardiff Blues: Halfpenny 2 pens