A 17-point contribution from Kiwi fullback Ben Blair helped see the Blues home and, if Leinster look to have the title wrapped up, the Cardiff-based region struck a major blow in the battle to be the top Welsh region.
The Blues, shrugging of last week's Heineken Cup disappointment, showed early willingness to give the ball some air, but were hit by a two-try blitz before the first five minutes had elapsed.
Acting captain Dwayne Peel, in his 50th league match, finished off a move he began and a break by fullback Ceiron Thomas was rounded off by young centre Jonathan Davies. Two conversions by Stephen Jones left the Blues stunned and they suffered again in a bad 60 seconds for the Robinson brothers.
A burst by centre Jamie ended with another addition to his long list of injuries, before brother Nicky fumbled a loose ball with the line at his mercy.
Aussie centre Marc Stcherbina was the next to knock on in the Scarlets' 22, but the visitors lost Alix Popham, yellow carded for an offence at the resulting scrum, and Blair's penalty put the home side on the board.
Fly half Robinson made up for his earlier error, crossing after good work by Gareth Thomas, but replacement Tom Shanklin and Thomas were both held up over the line as the Blues piled on the pressure.
They were finally rewarded when scrum half Jason Spice sent wing Tom James over for his eighth try of the season. Blair's kick gave the Blues an unexpected interval lead.
James was the Blues' hero again after the break when he set off on a 50-yard gallop through the Scarlets defence and put the supporting Stcherbina under the posts. Blair added the extras.
The departure of Spice to the sin-bin offered the Scarlets an opportunity to hit back and they grabbed it, a superb run by replacement fullback Morgan Stoddart allowing Wales's Grand Slam winger Mark Jones to fly in.
Within two minutes, the Scarlets were back in the lead, with a bonus point to boot, as Stoddart rounded off a length-of-the-field move and Stephen Jones converted.
Spice never returned, being replaced by Richie Rees, who immediately made a sniping run which almost reached the line before Mark Jones became the third player carded for preventing an early release. Blair's penalty put the Blues back in front.
When the Blues' all-action flanker Maama Molitika stole a Scarlet line-out and Blair crossed on the opposite touchline the home side also claimed a bonus point. A Nicky Robinson drop-goal completed the scoring, rounding off a fine performance in his first start since December, and robbing the visitors of a losing bonus point they had probably deserved.
Click Here for a Statistical Match Report from the Cardiff Blues v Llanelli Scarlets clash