The home side led 11-7 at half-time thanks to an Ellis Jenkins try and the boot of Gareth Anscombe.
However, former Cardiff Blues favourite Rhys Patchell returned to haunt his old side as he added to Tom Prydie’s first-half try to put the visitors back in front.
Despite long periods of pressure the Blues were unable to produce a winning opportunity as the reigning champions clung on.
The Blues were led onto the pitch by Taufa’ao Filise - hand-in-hand with his three children Sila, Liz and Ben – on his 250th appearance for the region and closely followed by Josh Navidi on his 150th.
Buoyed by the capacity crowd, the Blues made a bruising start to the encounter and they were rewarded for their endeavour when Gareth Anscombe slotted a simple penalty.
With the game being played at a ferocious pace, the alarm bells rang minutes later as the ball came loose on two occasions with the Scarlets hacking on but Matthew Rees proved the unlikely saviour.
The Blues were dealt a blow soon after when inspirational number eight Nick Williams was forced off after beating Leigh Halfpenny to a high ball and landing heavy.
He was replaced by Ellis Jenkins, who made his long-awaited return to action following a ruptured hamstring.
Despite the bright start it was the Scarlets who claimed the opening try. After flexing their muscle at a scrum on the 22, Gareth Davies broke off the back and found Tom Prydie with a fine off-load.
Cardiff Blues continued to throw everything at the Scarlets and following a succession of high tackles they were finally rewarded with a penalty.
They kicked to the corner and the Scarlets infringed once more with Anscombe going back to the corner.
The Blues set up a rampaging driving lineout and it appeared as though Matthew Rees had driven over against his former side. He was agonisingly short but Jenkins quickly recycled the ball and drove over.
Anscombe missed the tricky conversion but the try had put his side back in front by a single-point.
Despite the Blues appearing to be in the ascent, the Scarlets always looked dangerous, particularly when loose.
It looked as though they had claimed a second try when the ball broke out of a powerful Blues scrum and Wales international Davies pounced but TMO replays showed flanker James Davies, strayed offside and kicked the ball out.
Anscombe soon stretched the hosts lead to 11-7 and the home side continued to control affairs, although the majority of their possession was around the half-way line and they weren’t quite able to break through despite threatening.
There was one final opportunity when Anscombe released Olly Robinson after a fine Owen Lane break but the flanker was ankle-tapped as he broke clear and lost possession.
The second half got underway at an equally ferocious pace and once again the Scarlets threatened on the counter.
It was the Blues in possession but when Anscombe’s chip was charged down the visitors went of the attack with a series of stunning offloads maintaining the momentum.
Wales’ Capital Region managed to cling on but the Scarlets maintained possession and following a sustained period of pressure, Cardiff Blues-product Rhys Patchell jinked over with another former favourite, Leigh Halfpenny converting.
Halfpenny was off target with a long-range penalty on 54 minutes and a thunderous hit from Lee-Lo on Hadleigh Parkes sparked the home side into life.
The clear out earned a penalty, which was kicked to the corner and another driving lineout was set-up.
Electric scrum-half Williams broke off the back and released Willis Halaholo with a sumptuous offload. He was held short but possession was maintained.
The Blues went through a number of phases before Williams crashed over but he was held up.
From the ensuing scrum and a pair of restarts the Blues attacked with a set move which saw Tom James released with a flick pass but it was well read by the Scarlets, who held him at bay.
Two phases later the Scarlets turned over possession and cleared but back came the home side.
The topsy-turvy nature of the high-quality encounter continued and just as the Scarlets appeared to take a stranglehold, Lee-Lo intercepted. However, he was unable to keep his feet.
It was now the Blues that looked razor-sharp on the counter-attack and they earned a penalty shortly after the hour mark.
With it just on the edge of Anscombe’s range, the fly-half went to the corner but the Blues were unable to manufacture a scoring opportunity.
However they threw hammer and tong at the Scarlets for the next 10 minutes and were rewarded with a kickable penalty when Beirne knocked on deliberately.
Despite appearing to be within replacement fly-half Jarrod Evans’ range, the ball was kicked to the corner and Lee-Lo sliced through, however George Clancey bizarrely ruled a forward pass.
Alex Cuthbert, another Cardiff Blues player returning to action, stormed into the Scarlets 22 in the final play, but his foot was forced on the touchline.