A controversial penalty try helped Scarlets to a narrow 16-13 Guinness PRO12 victory over Ulster at a rain-drenched Parc y Scarlets.
World Rugby's new high-tackle directives, which came into play on January 3, had a crucial impact on the match when Scarlets were awarded a penalty try in the second half which also saw Ulster's Sean Reidy sent to the sin bin by referee Marius Mitrea for a high tackle on replacement scrum-half Aled Davies.
Fourth-placed Scarlets' pursuit of victory was also aided by 11 points from the boot of outside-half Dan Jones.
In the first half Ulster, who had to settle for a losing bonus point, had looked in control after wing Jacob Stockdale had gone over with outside-half Paddy Jackson supplying two penalties and a conversion.
For Scarlets, James Davies returned after serving a three-week ban and hooker Ken Owens was also back.
But they were without prop Samson Lee (calf), centre Scott Williams (rested) and fly-half Rhys Patchell, who could be out for 12 weeks if he needs surgery.
Rory Best, Iain Henderson, Paddy Jackson and Luke Marshall all returned for Ulster but Ruan Pienaar was injured. In a match played in steady rain, Ulster took a 13-6 lead into half-time as Scarlets struggled to break down the visitors' defence as well as making too many handling errors.
But Scarlets dominated the early exchanges and should have had a try as early as the fourth minute when Jones charged down a Jackson kick only for the Ulster No.10 to beat his opposite number to the loose ball.
Jones went some way to making up for the missed opportunity as he kicked two penalties after 11 and 14 minutes as Scarlets took a 6-0 lead.
After Jackson kicked his first penalty in the 17th minute, Ulster scored the only try of the half. Following a drive from a line-out the ball went out to centre Stuart McCloskey and he put Stockdale over for a simple try as Scarlets' defence was nowhere.
Ulster continued to play the conditions better than the home side and were rewarded with a second Jackson penalty with the final kick of the half. Scarlets were forced into a change at the break when scrum-half Gareth Davies was replaced by Aled Davies due to injury.
The home side eventually got some good field position and were rewarded with a penalty which Jones kicked to reduce the deficit to four points.
But the key moment of the match came after 61 minutes when replacement scrum-half Davies went for the try line only to be adjudged to have been high-tackled going for the line.
After TMO Carlo Damasco reviewed the incident, referee Mitrea used the new tackle laws by awarding a penalty try and issuing Reidy a yellow card.
Jones converted as Scarlets went into the lead for the first time. Two minutes later there was more controversy as Jake Ball was also yellow-carded for a high tackle on flanker Clive Ross, but Scarlets held on for the victory.