Navidi covered every blade of grass in the first half both in attack and defence and along with Lou Reed produced an opening half of vim and vigour to leave the Scarlets chasing their tails at the break.
The only disappointment for Mark Hammett’s side is the fact they were unable to score a single point after the interval.
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 derby was a feisty affair with Cardiff Blues lock Filo Paulo and Scarlets second row Johan Snyman sin-binned for a scuffle as the match hotted up.
Gareth Anscombe knocked over 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 before Navidi got on the score sheet for the second time of the match when he powered over from close range.
Anscombe added a third penalty when Rob McCusker made a late tackle on Reed after the lock had made a great break out of his own 22.
The Scarlets tried to play their way back into the game but a series of dropped passes, knock-ons and poor decision making ensured a disappointing trip back up the M4.
