Ospreys produced a determined defensive display to grind out a deserved 10-6 derby win at Parc y Scarlets on Boxing Day.
Rhys Priestland kicked a penalty in each half for the hosts and Dan Biggar notched one of his own, in an uncharacteristically wayward kicking display.
Hanno Dirksen had been denied a second-half try by the TMO but replacement Ian Evans did get the decisive score to win it for Ospreys late on.
Ospreys ventured into opposition territory early on but after kicking his side clear and reversing the early momentum, Priestland put the hosts on the board with a penalty after seven minutes.
Scarlets were handed the chance to double the lead eight minutes later, after the visiting front row stood up in the scrum, but Frazier Climo’s halfway-line effort struck the post.
Rhys Webb led the Ospreys fightback, sending a neat low kick into the hosts’ 22 but full-back Liam Williams collected and ran his side out of immediate danger, before Biggar sent a 35-yard drop-goal wide.
Williams was then on hand again to bail out Scarlets, picking up a chip-kick deep in the corner and sending a perfect clearance into the opposition half, bouncing into touch.
Ospreys trailed but continued to attack with more intensity, Biggar orchestrating waves of pressure, but stern defending and sloppy handling undid much of the good work.
It wasn’t until 36 minutes that they earned the opportunity to draw level, when Biggar pointed to the posts from halfway, but the penalty fell short and left and Scarlets went into the break ahead.
It took just a minute of the second-half for Ospreys to earn another penalty but Biggar missed his second of the afternoon, this time a far simpler effort.
Visiting attacks continued to fall flat as a string of handling errors gave Scarlets possession but when it was their turn to burrow into the Ospreys’ 22 there was no way through.
Priestland finally added three more points, after 49 minutes, following an infringement in the lineout from Ospreys second row Alun Wyn Jones.
And the game burst into life shortly before the hour mark, as Ospreys got the ball out wide to Dirksen and his diving effort prompted a lengthy deliberation from the TMO.
The wing launched himself at the corner, under pressure from two Scarlets defenders, and he was adjudged to have slipped narrowly into touch on his way to the line.
Shortly after taking to the pitch Rhodri Jones was penalised for not rolling away and Biggar had a third bite of the cherry, eventually getting his side on the board.
Opsreys did eventually touch down five minutes from time, when Biggar’s inch-perfect kick set the pack up to drive towards the line and Evans bundled over – Biggar added the conversion.
Priestland responded by kicking Scarlets back into the visitors’ half and waves of pressure saw the visitors concede a string of penalties, which resulted in man-of-the-match Jones being sent to the sin bin.
The hosts kicked for the line once more, needing a try to win it, but the 14 men held firm in a resilient display of aggression.