The Scarlets claimed their first victory at the Cardiff City Stadium and ended the Cardiff Blues' unbeaten home record as they moved up to second in the Magners League table with a 16-10 triumph.
A try, conversion and penalty from fly-half Ceri Sweeney gave the hosts a 10-9 interval lead, Rhys Priestland kicking three penalties for the Scarlets.
But Wales ace Stephen Jones came off the bench for the Scarlets to create a superb match winning try for Priestland with a rare moment of brilliance in a low-quality encounter.
The place kicking was hit and miss throughout and the pattern was set in the opening quarter, when the Blues Sweeney and Scarlets opposite number Priestland each kicked one and missed one, while Blues wing Leigh Halfpenny was wide with a long distance effort.
The visitors lost winger Morgan Stoddart to the sin-bin after a couple of dangerous tackles, the second ending the proceedings for Blues' wing Tom James. The Blues took advantage when lively scrum half Richie Rees darted through a half-gap and offloaded for Sweeney to touch down next to the posts, making his conversion a simple matter.
Referee Tim Hayes then evened the numbers up with a yellow card for retaliation by flanker Andries Pretorius, but Priestland was off target with the resultant penalty.
The Scarlets acting skipper, Sean Lamont, grabbed a loose ball deep in his own half, sparking a move which saw the newly-returned Stoddart held up just short. The visitors kept hammering away, but prop Iestyn Thomas was ruled by the television official to have lost the ball as he touched down.
After the Blues again lost a man - scrum-half Rees, carded for a deliberate knock-on - Priestland further punished them with another penalty.
Television replays aided the Blues once more as the video referee ruled out a try by Scarlets debutant Ben Morgan and the 14-man hosts survived early pressure on the restart, before the game settled into a war of attrition. But shortly after the hour mark, the visitors produced the game's one moment of flair.
Jones, brought into the action to provide some control, floated a kick towards the left touchline, the giant Lamont palmed it inside and Priestland, now at full-back, raced through to score. Jones converted and the Scarlets held on, despite a long-range penalty miss from Priestland and a last-minute yellow card for replacement lock Dominic Day.