The Scarlets ground out a Celtic League victory in atrocious conditions at the Arms Park on Saturday.
Two Gareth Bowen penalty goals settled the issue in a tryless affair in the Cardiff mud and rain.
The scoreline was an incredible 0-0 at halftime as the conditions prevented the running rugby that both sides have produced in recent weeks.
The Scarlets were down to 14 men on two occasions when backrower Chris Wyatt and scrum-half Mike Phillips being shown the yellow card by referee Donal Courtney, but the Blues couldn't take advantage on the slippery pitch.
Scarlets fly-half Bowen finally gave the scorers something to do with a well-struck 47th-minute penalty goal, and doubled the margin in the 68th as the visitors kept their nerve in the awful conditions.
The result brings to and the Blues' five-game winning streak, and means the Scarlets keep in touch with league leaders Ulster.
Cardiff Blues: 0.
Llanelli Scarlets: Pens- G Bowen 2. Halftime: 0-0.