Fly-half Owen Williams kicked all Scarlets' points as the the Welsh side claimed a RaboDirect Pro 12 double over Munster at Parc y Scarlets.
Ronan O'Gara only managed one penalty from four attempts for the visitors, although he did convert wing Denis Hurley's late consolation try.
Both sides had Six Nations squad members in their line-ups. Munster were boosted by the inclusion of Donncha O'Callaghan and O'Gara, while the Scarlets included Josh Turnbull and Liam Williams.
O'Gara had a testing early kick after the Scarlets were penalised on halfway, but he left his effort hanging short of the target.
It was not a great start for the fly-half and things did not improve. The Scarlets were caught offside in front of their posts, but again O'Gara failed with his kick from 35 metres out, the ball rebounding off the left upright.
While O'Gara struggled to find his range' his opposite number Owen Williams opened the scoring with a sweetly struck penalty on 14 minutes.
Owen Williams was short with another attempt inside his half, but back on target with his third shot on 18 minutes to double the Scarlets' lead.
Eventually Munster got a foothold in Scarlets territory, with O'Gara finally on target with a 29th-minute penalty from 25 metres out after the home side were penalised at a scrum.
But that was cancelled out by the in-form Owen Williams, who kicked a fine 55-metre penalty to give the Scarlets a 9-3 interval lead.
Munster's discipline let them down at the start of the second half with wing Johne Murphy conceding a penalty for a clash with Phil John, but fortunately for the Irish side Owen Williams was off target with his penalty kick.
But Munster still continued to struggle. Owen Williams kicked his fourth penalty, while O'Gara missed his third from four attempts.
It got even worse for the Irish as captain Mike Sherry was sin-binned on 56 minutes, allowing Owen Williams to kick a fifth penalty as Scarlets led 15-3.
And down to 14 men Munster went further behind to an Owen Williams drop goal after 64 minutes.
Munster at least had the final word after Owen Williams blotted his copybook by getting sin-binned, wing Hurley going over for the only try of the contest.
O'Gara kicked the conversion, but Scarlets were good value for their win.