Ospreys completed a RaboDirect Pro12 double over rivals Scarlets at the Liberty Stadium to move up a place to second in the table.
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First-half tries from centre Ashley Beck and wing Aisea Natoga were enough for them to hang on for a 17-12 win despite visiting fly-half Rhys Priestland kicking three second-half penalties.
The match just came just eight days after Ospreys had won 10-6 at Parc y Scarlets.
Prop Duncan Jones celebrated his 200th appearance for the region, with Wales international forwards Ian Evans and Aaron Jarvis recalled while Adam Jones was on the bench and Justin Tipuric was a late withdrawal.
For Scarlets, Wales hooker Ken Owens and full-back Liam Williams were injury absentees, although Rhodri Williams came in at scrum-half and Josh Turnbull started at flanker.
Ospreys had the better of the first half in difficult conditions and deserved their 14-3 interval lead.
Priestland had a chance to put Scarlets into the lead after five minutes but his penalty kick fell short of the posts.
In a half dominated by tactical kicking, it took a bit of magic by Ospreys scrum-half Rhys Webb to break through the away defence to set up the first try.
He linked with full-back Sam Davies and, at the breakdown, Beck touched down by the posts. Fly-half Dan Biggar converted.
Two minutes from the half-time, Scarlets got on the board with a Priestland penalty.
But a kick a great kick to touch by Biggar gave Ospreys good field position from which they grabbed their second try when Davies put over Natoga on the right for the Fijian's first Pro12 score.
Five minutes into the second half, Biggar kicked a penalty to open up a 14-point lead.
But that was Ospreys last score of the contest as they slowly lost the territorial battle.
Priestland kicked the visitors back into contention as Ospreys lost their way, not helped by Natoga being yellow-carded by Welsh referee Nigel Owens for a deliberate knock-on.
Scarlets went in search of a vital try but Ospreys held on to secure their fourth straight win in all competitions.