Welsh internationals George North and Jonathan Davies proved the difference as the Scarlets edged past a brave Newport Gwent Dragons side in the first part of Judgement Day.
North scored a try in each half while Davies crossed after the interval as their side emerged 20-28 winners at the Millennium Stadium.
It was a game Simon Easterby's side perhaps should have won by more but the Dragons refused to lie down, their defence giving the Scarlets little throughout a keenly contested encounter.
Half backs Jonathan and Dan Evans scored a try apiece with Tom Prydie kicking the rest of the Dragons' points. But despite their best efforts, the international class of North and Davies secured the win.
Owen Williams had a mixed day with the boot but added 13 points as the Scarlets maintained their PRO12 play-off hopes.
The Scarlets had started quickly and dominated the early exchanges save for one break for the Dragons from Will Harries. The right wing skipped round the tackle of Liam Williams but was tackled into touch by the covering Aled Davies.
That attack apart, Easterby's side were dominating both possession and territory. Owen Williams put an 11th minute penalty effort wide and had earlier kicked to touch when a pot at goal looked on. But the Dragons' defence, led by Dan Lydiate, was withstanding anything the Scarlets could throw at them as the game remained scoreless.
The Dragons may have been level but they were conceding a number of penalties in doing so and referee Peter Fitzgibbon finally lost patience, sending Welsh No. 8 Toby Faletau to the sin bin with 18 minutes gone.
And with the Dragons down to 14 men, the men in red took advantage. A clearance kick from Dan Evans was returned with interest by Owen Williams. He found Aled Davies in support who popped the ball up superbly to the supporting North. With open spaces in front of him, the Wales wing needed no second invitation and finished superbly to extend his side's lead.
Owen Williams converted but struck the left hand post with a penalty as his side failed to move out of sight.
The Dragons had made little inroad into the opposition half but with minutes of the first half remaining, they soon found themselves back in the game. When scrum half Jonathan Evans picked the ball up at the base of a ruck, there looked very little danger. But with the Scarlets lacking guards around the ruck, he threw a lovely dummy to leave prop Phil John trailing in his wake as he sprinted in to score.
Prydie added the extra two and a penalty with the last kick of the half to leave things level at the break.
Given their dominance of most of the first period, the Scarlets must have been disappointed to not have been ahead. But a simple Owen Williams penalty, minutes after half time, restored a three point cushion.
On his 26th birthday, Harries was providing the Dragons' best attacking option as he constantly threatened with ball in hand. And when the Scarlets turned over ball, the former Wales man nearly finished off what would have been a length of the field move.
The impressive Dan Evans started the move, bursting through a Scott Williams tackle to feed the supporting Harries. At full tilt though, he failed to find Patrick Leach outside him and the chance was lost.
In contrast to the first period, the momentum was now with the Dragons and Prydie soon levelled things up with his second penalty. It was nip and tuck with little between the teams but from the restart, it was the Scarlets who stepped things up a notch.
Owen Williams kicked his third penalty and struck the post with another effort before the Scarlets struck two quick blows to win the game. Jonathan Davies went over for his side's second try following a Scott Williams break, the score particularly remarkable given that the Wales centre was facing the wrong way and under pressure from Faletau.
TMO Tony Rowlands had to confirm the score but it soon got better for the Scarlets. Owen Williams converted the score and from the restart, his side added their third try. Ken Owens, who had replaced Matthew Rees at half time, fed North who sprinted in down the right hand touchline.
At 28-13, the game looked up but as they had done all game, the Dragons refused to lie down with Dan Evans squeezing over for a score which Prydie converted.
It was not enough to win it but the Scarlets certainly knew they had been in a contest.