Despite trailing to an early Leigh Halfpenny penalty, two scores from Davies and another great individual effort from Lee Williams gave Scarlets the victory in a game that also marked the return of Rhys Priestland.
Scarlets came into the game boasting a four-game winning streak in the RaboDirect PRO12 and after Ospreys had failed to pick up any points against Glasgow Warriors on Friday, they knew a win would move them up into fourth spot.
And the importance of the occasion was seen immediately with a frantic start to the game, the initial few exchanges were packed full of turnover ball and end-to-end action as Cardiff's Harry Robinson made a few exciting breaks.
Scarlets fly-half Owen Williams had the first attempt at goal from just inside his own half on nine minutes, but while his monster effort didn't lack power, it sailed just wide of the posts.
The first points didn't arrive until the 17th minute when a late tackle gave Welsh full-back Halfpenny the chance to give Cardiff the lead with a penalty which he duly took.
But play-off chasing Scarlets responded with the game's first try as Davies bundled over for his first score, cutting through the defence with ease as Williams added the extras for a 7-3 lead after 26 minutes.
Lou Reed almost provided a response for the visitors but was cut down just short of the line on 32 minutes. Halfpenny bagging his second penalty of the night after Scarlets were penalised a few phases of play later.
Williams then kicked another penalty after the Blues scrum was accused of not driving straight and that was the last action of the half as the hosts held a 10-6 advantage.
After the break Scarlets began to take the game away from their Welsh rivals, Davies grabbing his second just before the hour and Williams added the extras to give his side an 11-point advantage with 20 minutes to play.
The returning Priestland replaced Williams at fly-half and his kicking was calling into action in very simple fashion after Williams had touched down beneath the posts for Scarlets' third try six minutes later after a great pick-up and sprint to the line.
With just one game remaining, Scarlets have opened up a four-point gap between them and Ospreys - the only side that can deny them a play-off semi-final appearance.
And victory over Treviso at Parc Y Scarlets next Friday evening will secure their spot in the play-offs and deny Ospreys the chance to defend their RaboDirect PRO12 title.
|Scarlets Score Card|
|Cardiff Blues Score Card|