Scarlets held on to claim an 18-13 RaboDirect Pro12 victory over leaders Munster, who were denied an unprecedented clean sweep of victories over the four Welsh regions.
The Munstermen had to settle for a losing bonus point which stretched their lead to three points over Leinster.
A try apiece from scrum-half Gareth Davies and flanker John Barclay were the back bone of the victory at Parc y Scarlets with Munster's only try coming from wing Gerhard van den Heever.
The match saw British & Irish Lions centre Jonathan Davies return for the Scarlets giving him an opportunity to prove his fitness ahead of Wales' RBS 6 Nations clash with England at Twickenham next Sunday.
Davies was back after recovering from a pectoral injury in Wales' defeat to South Africa last November. He partnered former England international Olly Barkley in midfield.
Leaders Munster, who had won all their previous seven games against the four regions, made eight changes from the side that beat the Ospreys last weekend.
Despite having most of the territory and possession in the first period, Scarlets found themselves frustratingly 13-8 behind at the break.
Munster had to soak up attack after attack in the opening quarter but the Scarlets had to settle for a 3-3 scoreline with Barkley and Ian Keatley having swapped penalties in the space of two minutes.
For all their intense pressure Scarlets were eventually rewarded with a try when scrum-half Gareth Davies scampered in after breaking down the blindside from a maul.
But all the hard work from the Welsh region was undone in the space of five minutes before half-time when a dropped pass by Barkley in midfield allowed Van den Heever to run in unopposed.
And on the stroke of half-time, a Scarlets infringement at a ruck allowed Keatley to kick a penalty to give the visitors a five-point cushion going in to the second half.
It all went Scarlets' way straight after the break.
Keatley missed a second minute penalty, while Aled Thomas was on target with his own penalty before Barclay ran in 60 metres after picking off scrum-half Duncan Williams' pass from a line-out.
But for much of the rest of the half the Scarlets were under the cosh especially when Josh Turnbull was sin-binned for a careless use of the boot.
Van den Heever thought he had a second try on 68 minutes but it was disallowed for an earlier knock-on by Williams at a ruck.