Scarlets took full advantage of a yellow card to Newport Gwent Dragons flanker Scott Matthews to clinch victory in this Welsh derby.
Skipper Rob McCusker and wing Chris Knight both crossed for tries while Matthews was in the sin-bin to put the home team in charge.
Dragons fly-half Kris Burton did get a try back, and contributed a conversion and penalty.
But his side did not recover from conceding 14 points in six minutes.
The match marked Welsh international McCusker's return to action after a month out with a calf injury.
Scarlets: Gareth Owen; Jordan Williams, Gareth Maule, Adam Warren, Chris Knight; Aled Thomas, Aled Davies; ,Shaun Hopkins, Kirby Myhill, Rhodri Jones, Johan Synman, Richard Kelly, Craig Price, Dan Thomas, Rob McCusker (capt).
Replacements: Darran Harris, Gareth Thomas, Ben Leung, Carwyn Jones, James Davies, Gareth Davies, Josh Lewis, Kristian Phillips.
NG Dragons: Dan Evans; Will Harries, Tyler Morgan, Ashley Smith, Matthew Pewtner; Kris Burton, Wayne Evans; Aaron Coundley, Elliot Dee, Francisco Chaparro, Joe Davies, Adam Jones (capt), Jevon Groves, Scott Matthews, Ieuan Jones.
Replacements: Hugh Gustafson, Nathan Williams, Nathan Buck, Rob Sidoli, Netani Talei, Luc Jones, Rhys Jones, Ashton Hewitt.