|Cardiff Blues (21) 21|
|Tries: Navidi 2 Con: Anscombe Pens: Anscombe 3|
|Scarlets (6) 9|
|Pens: Priestland 3|
Josh Navidi helped Cardiff Blues claim the honours over Scarlets in the first Welsh derby of the Christmas period.
The number eight scored two tries in a dominant first-half display by Blues at their Cardiff Arms Park home.
Gareth Anscombe added three penalties and a conversion, with Rhys Priestland replying for Scarlets with six points.
Scarlets kept Blues scoreless after the break, but wasted gilt-edged chances to claim tries and could only manage a third Priestland penalty.
It was a much-needed win for ninth-placed Blues - who saw prop Taufa'ao Filise come off the bench to make a record 183rd appearance for them - that took them to within six points of Scarlets, who remain seventh in the Pro12 table.
The visitors were already without Wales full-back Liam Williams for the game, but had lock Jake Ball and flanker Aaron Shingler pull out at late notice because of illness.
That saw a reshuffle with George Earle coming into the Scarlets second row, while Lewis Rawlins was promoted from the bench to make his first league start at six.
Blues were also missing a Wales cap in injured scrum-half Lloyd Williams, with his place going to Lewis Jones.
But the hosts made light of the form book to make an impressive start to the game, with Anscombe converting two early penalty chances before the game's opening try.
Navidi picked up from the base of a five-metre scrum and drove forward before his fellow forwards arrived for the final shunt that saw him over the try-line.
Anscombe converted to make it 13-0, although Priestland replied with two penalties as Scarlets put the ball through the hands to gain territory and exert pressure on Blues.
The relief was short-lived, though, as Blues drove from an attacking line-out on the left and number eight Navidi again showed great power to claim his second try.
Fly-half Anscombe could not add the conversion but the New Zealander added a third penalty soon after, when Rob McCusker made a late tackle on Lou Reed after the lock had made a great break out of his own 22.
The derby atmosphere boiled over soon after half-time when rival locks Filo Paulo of the Blues and Johan Snyman of the Scarlets came to blows, with referee Dudley Phillips sending the two heavyweights to cool off in the sin-bin for 10 minutes.
With peace restored and both sides a man short up front, the backs took centre stage and the crowd were treated to thrust and counter-thrust as the Welsh rivals probed for an opening.
Scarlets shaded that encounter and their reward was a third Priestland penalty that cut the deficit to 21-9.
After Anscombe missed a penalty for Blues, they also had the misfortune of losing hooker Kristian Dacey to a twisted knee - although that saw Matthew Rees come off the bench to make an all-Lions front row alongside Gethin Jenkins and Adam Jones.
While Blues were flexing their muscles up front, Scarlets were starting to show their teeth behind and first Priestland and then Scott Williams made clean breaks that should have resulted in tries.
First Rhodri Williams could not hold onto the inside pass from Priestland, then Williams found himself isolated as his team-mates were too slow to support the centre.
With those two wasted opportunities and a late chance for Michael Tagicakibau, Scarlets' best hopes of victory evaporated, despite a late sin-binning for Navidi that slightly spoiled his man-of-the-match award.
Cardiff Blues: Joaquin Tuculet; Alex Cuthbert, Cory Allen, Adam Thomas, Lucas Amorosino; Gareth Anscombe, Lewis Jones; Gethin Jenkins (capt), Kristian Dacey, Adam Jones, Filo Paulo, Lou Reed, Josh Turnbull, Sam Warburton, Josh Navidi.
Replacements: Matthew Rees, Sam Hobbs, Taufa'ao Filise for A. Jones (71), Macauley Cook for Reed (53), Manoa Vosawai for Turnbull (55), Tavis Knoyle for L. Jones (71), Gareth Davies for A. Thomas (78), Tom Isaacs for Gonzalez-Amorosino (62).
Sin Bin: Paulo (42), Navidi (75).
Scarlets: Steffan Evans; Harry Robinson, Regan King, Scott Williams (capt), Michael Tagicakibau; Rhys Priestland, Aled Davies; Rob Evans, Emyr Phillips, Samson Lee, George Earle, Johan Snyman, Lewis Rawlins, James Davies, Rob McCusker.
Replacements: Kirby Myhill for E. Phillips (72), Wyn Jones for R. Evans (72), Rhodri Jones, Rory Pitman for Rawlins (50), Will Boyde, Rhodri Williams for A. Davies (59), Steven Shingler for Priestland (69), Hadleigh Parkes for S. Evans (67).
Sin Bin: Snyman (42).
Referee: Dudley Phillips (IRFU)
Assistant Referees: Neil Hennessy, Sean Brickell (both WRU)
Citing Commissioner: Ray Wilton (WRU)
TMO: Gareth Simmonds (WRU)