The win saw the Blues haul themselves up into fourth place, while the Scarlets have slipped to fifth, but with two games in hand over Magners League leaders Ulster.
With just one more game before they travel to Ulster to protect their unblemished Heineken Cup record in a fortnight, the Scarlets will want a win at Edinburgh on Friday to restore their bruised confidence.
Scarlets Head Coach Phil Davies will hope Wales Captain and Scarlets fly-half Stephen Jones shakes off his troublesome back spasms injury as quickly as possible. Jones’s understudy Ceiron Thomas faltered at times in Cardiff, as he did against the Ospreys, and was one of two first half Scarlets yellow cards as ill discipline saw the guests 17-0 down at half-time.
With the start of the New Year came the new scrummaging regulations designed to reduce the force on impact and the rule change seemed to de-power the scrums. This helped the Scarlets after their pack was reduced to seven men when flanker Dafydd Jones was shown an early yellow card.
In his absence, Blues fullback Ben Blair kicked a penalty for the Blues, but the Scarlets were dealt a hammer blow on the half hour mark when Blues fly half Nicky Robinson glided through the defence before chipping to the corner.
In a desperate bid to stop him, Thomas earned a yellow card for trying to hold him back and referee Hugh Watkins had no option but to award a penalty try and Blair slotted the conversion.
The home side took full advantage of the extra numbers behind the scrum by moving the ball wide for exciting prospect Tom James to cut back inside through two tackles. His try under the posts gave Blair an easy conversion and he extended their lead to take the Blues into a 17-0 lead at the break.
With a heavy deficit to make up, the Scarlets came out firing and Thomas kicked a forty-third minute penalty. Yet normal service was quickly restored when the Blues pack smashed their way to the line for their man-of-the-match flanker Scott Morgan to barge his way over and the home side was cruising at 24-3 with half an hour to play.
The Scarlets rallied, but the Blues were never seriously threatened, even when they lost Morgan to the sin bin for collapsing a maul.
The guests were later awarded a consolation penalty try when the entire Blues front-row stood up at a scrum on their own line, but a fourth try by wing Chris Czekaj near full time gave the Blues a deserved bonus point win.
