A pulsating opening 40 minutes from the home side saw Blues storm into a 21-6 lead with two tries from back row Josh Navidi.
It was an irresistible opening half as Blues controlled territory and possession to confidently build up a lead through the assured kicking of Gareth Anscombe and a powerful forward show.
The second half was a contrasting affair as Scarlets turned the screw and looked to find a way back into the Black Friday encounter in front of a vocal and partisan crowd of 9,443.
However, Mark Hammett’s men refused to be breached and despite playing for spells with Filo Paulo and Navidi in the sin bin a superb resolute defensive show ensured the points would remain in the capital.
Blues made a number of changes for the league clash with Argentina duo Lucas Amorosino and Joaquin Tuculet returning while Lou Reed and Kristian Dacey also won call-ups for the big East versus West showdown.
Hooker Dacey was straight into the action as he picked off the first stray Scarlets lineout before the new-look home backline went to work with Tuculet, Amorosino and Alex Cuthbert prominent.
Navidi, twice man-of-the-match in previous home games, was once again to the fore as his dynamic ball carrying saw him twice thump into contact and break tackles roared on by the home faithful.
The first scrum of the game saw Blues wheel the visitors to win the put in and from the second a penalty was secured as the Scarlets front row popped up. Anscombe lined up his first kick of the game and duly sent it over, via the left upright, for a 3-0 lead.
Blues were enjoying their best start to any game this season as they controlled all aspects of the game with Cory Allen picking a difficult pass up off his feet before Cuthbert and Sam Warburton rattled on and Josh Turnbull, against his old region, powered down the right wing.
It was an intense, direct and high tempo start from Blues and a penalty for a high tackle gave Anscombe his second successful kick of the night to double the lead.
The kicking game of Blues was clicking in decisive fashion as Tuculet produced a peach over Harry Robinson’s head to clear danger before Anscombe went one better with a drilled low effort into the far corner that Rhys Priestland could do nothing to stop.
From the resulting lineout five-metres out, Scarlets lost ball and Blues struck for the game’s first try in dominant style.
Navidi picked up at the back of a scrum and, after initially being halted, he was joined by his team-mates who powerfully shunted him over the line and down for a 13-0 lead to the backdrop of thundering cheers from the home fans.
Shell-shocked Scarlets needed a response and a powerful run from Regan King secured a penalty that Priestland nudged over. Two minutes later a brilliant run from Rob McCusker set up another penalty and Welsh ace Priestland did the rest to the cut the lead to 13-6.
Back came Blues with the elusive Tuculet cutting a sublime line to force Scarlets back before the full back again broke clear and flicked the ball wide to countryman Amorosino who intelligently grubber kicked in behind and forced Steffan Evans to hurriedly kick the ball out.
The resulting lineout was duly gathered and the forwards again powered through the gears and Navidi crashed over from the driving maul for his second of the night.
It was all action as lock Reed stormed down the middle and fed Dacey on his shoulder to a huge ovation. Moments later Turnbull repeated the feat as he bashed through tackles and when the penalty was secured at the breakdown Anscombe did the rest for a 21-6 half-time lead.
Fired up Scarlets looked to start the second half at real pace before tempers flared between Filo Paulo and Johan Snyman and the referee went to the TMO before both players were yellow carded for the scuffle.
Priestland nudged over a penalty to cut the lead to 21-9, but Blues still looked lethal with ball in hand as Navidi barreled past men and supporting runner Warburton arched his run and fed Allen who grubber kicked in behind to win a lineout.
Scarlets, though, were now beginning to throw the ball around to try and force an opening with a knock on the left wing denying them what looked a certain score after they exploited an overlap with deep dummy runners.
A superb chase by Cuthbert, to a steep high bomb kick from Lewis Jones, secured a penalty to stem the long periods of territory that Scarlets had enjoyed. But Anscombe saw his effort at the posts pull up short of the target.
A break down the left flank orchestrated by Priestland almost set Scarlets away again, but this time replacement scrum half Rhodri Williams could not cling onto the final pass in contact just moments after coming on the field.
Visiting skipper Scott Williams then raced into space and clear, but as he looked to pick out a supporting colleague on the left all he did was float a pass into the grateful hands of Cuthbert on the wing.
Prop legend Filise came on for his 183
rd record breaking appearance to a huge ovation as Blues looked to empty the bench and bring fresh legs into derby battle.
The home side continued to battle for every ball, but were down a man when Navidi was sent to the sin bin for a tip tackle after referee Dudley Phillips consulted with his TMO.
Scarlets rolled the dice one more time with wing Michael Tagicakibau dragged into touch by a superb tackle and even a late flurry in injury time could not breach the Blues’ rearguard as the hosts claimed derby spoils to launch the festive season with a crucial win.
Timeline:
06m Anscombe p 3-0
12m Anscombe p 6-0
19m Navidi t Anscombe c 13-0
23m Priestland p 13-3
25m Priestland p 13-6
29m Navidi t 18-6
33m Anscombe p 21-6
50m Priestland p 21-9
Cardiff Blues: 15 Joaquin Tuculet, 14 Alex Cuthbert, 13 Cory Allen (Isaacs 62), 12 Adam Thomas (Davies 78), 11 Lucas Amorosino, 10 Gareth Anscombe, 9 Lewis Jones (Knoyle 71), 1 Gethin Jenkins (Hobbs 72), 2 Kristian Dacey (Rees 60), 3 Adam Jones (Filise 71), 4 Filo Paulo, 5 Lou Reed (Cook 53), 6 Josh Turnbull (Vosawai 55-64, 75), 7 Sam Warburton, 8 Josh Navidi
Replacements: 16 Matthew Rees, 17 Sam Hobbs, 18 Taufa’ao Filise, 19 Macauley Cook, 20 Manoa Vosawai, 21 Tavis Knoyle, 22 Gareth Davies, 23 Tom Isaacs