Scarlets edge Blues
The wing scored once and had a major part in the hosts other effort, their two tries narrowly enough to take the spoils as conditions ensured a difficult game for both sides.
Willis Halahalo scored in the second half to set up a nervy finish, the latest try in a game of brilliant finishing, as both sides made the most of minimal chances.
But it was Scarlets who held their own, enough to go fifth in the Pro12, while the gap between Blues and the top six now sits at five points.
Both sides struggled to find their feet as the swirling wind proved havoc, encouraging ball-in-hand rugby at Parc y Scarlets, much to the delight of the home faithful.
But while phases were lengthy, chances were at a premium despite numerous breaks, but that all changed as some delightful Patchell skill opened the scoring.
Taking a high ball deep in his half, the flyhalf crossed halfway before support came in the form of Johnny McNicholl, temporarily strengthening the left wing as Scarlets suddenly boasted numerical advantage.
He in turn found Evans, and after orchestrating a clever dummy of his own, the fellow wing was through to dot down in the corner for the game's first points.
With conditions as they were, it seemed mistakes could become crucial as the game wore on, though Patchell made up for his missed conversion to put Scarlets more than a score ahead with a penalty, 8-0 after Blues came in from the side.
They responded immediately with a penalty of their own though as Steve Shingler took advantage of a rare Jonathan Davies error, knocking on from the restart as the visitors were able to build up a head of steam heading to the interval.
But it took just six minutes of the second half for the stuffing to be knocked out, with Evans following up his own score to set up Williams for a second try.
A brisk turn of place saw Evans marauding through with no trouble before finding Davies on the left, firing back inside to set centre partner Williams away, the Scarlets once again dotting down from deep, with Patchell adding the extras.
But Blues showed they were not out of the game, Shingler this time making the most of a kick to manoeuvre his way forward with the help of Lloyd Williams.
There was still plenty to do when the baton was handed to Halahalo, but some quick-thinking saw the centre sidestep the last man to close the gap to five points.
It seemed Blues would come again moments later, but some excellent intuition from McNicholl led to an interception, shifting back the momentum with 20 minutes remaining.
Yet despite both teams pushing hard, 15-10 was how the score was to remain, with Aled Thomas' late penalty falling wide to give Scarlets spoils and bragging rights on home soil.
The scorers:
For Scarlets:
Tries: S Evans, Williams
Con: Patchell
Pen: Patchell
For Cardiff Blues:
Try: Halaholo
Con: Shingler
Pen: Shingler
Teams:
Scarlets: 15 Aled Thomas, 14 Johnny McNicholl, 13 Jonathan Davies, 12 Scott Williams (captain), 11 Steff Evans, 10 Rhys Patchell, 9 Jonathan Evans, 8 John Barclay, 7 Will Boyde, 6 Tadhg Beirne, 5 Lewis Rawlins, 4 Jake Ball, 3 Samson Lee, 2 Ryan Elias, 1 Wyn Jones.
Replacements: 16 Emyr Phillips, 17 Rob Evans, 18 Werner Kruger, 19 Tom Price, 20 Josh Macleod, 21 Gareth Davies, 22 Dan Jones, 23 Hadleigh Parkes.
Cardiff Blues: 15 Matthew Morgan, 14 Alex Cuthbert, 13 Rey Lee-Lo, 12 Willis Halaholo, 11 Rhun Williams, 10 Steve Shingler, 9 Lloyd Williams, 8 Nick Williams, 7 Sam Warburton (c), 6 Josh Navidi, 5 James Down, 4 Macauley Cook, 3 Taufa'ao Filise, 2 Kristian Dacey, 1 Rhys Gill.
Replacements: 16 Kirby Myhill, 17 Brad Thyer, 18 Scott Andrews, 19 Jarrad Hoeata, 20 Ellis Jenkins, 21 Tomos Williams, 22 Nicky Robinson, 23 Cory Allen.
Referee: Nigel Owens
Assistant Referees: Craig Evans, Jon Hardy
TMO: Paul Adams
@PRO12rugby
