Ospreys resisted a Scarlets fight back to win the Guinness PRO12 Welsh derby at the Liberty Stadium 17-15 and go back to the top of the table.
Tries from Aisea Natoga and Dan Lydiate, on his first start for the region, put the Ospreys in a strong position at 17-9 at the break.
But the Scarlets, despite losing Rhys Priestland through injury in the first half, got within two points with two second-half penalties for Steven Shingler.
Ospreys held on to win and it means Scarlets have only won once at the Liberty Stadium back in September 2007.
Lydiate made his first start for Ospreys with blindside James King moving to partner Alun Wyn Jones in the second row in place of Rynier Bernardo - the only change from the side that beat Ulster 31-20.
Despite recent injuries, Wales internationals Liam Williams and Priestland both started along with captain John Barclay, who made his comeback from a thigh strain. Aaron Shingler returned from illness while Hadleigh Parkes made his first start for the region.
It was an incident packed first half as one would expect in a hard fought Christmas derby with an early yellow card while the TMO Derek Bevan was called upon three times to adjudicate on tries.
There was also an early injury which forced Priestland off the field but not before he had given the Scarlets the lead with an eighth minute penalty.
But in heavy rain the visitors were soon down to 14 men when Kristian Phillips was sent to the sin bin for a tip-tackle on Ospreys full-back Dan Evans.
Dan Biggar and Steven Shingler swapped penalties before replacement wing Aisea Natoga slid in after a break by Hanno Dirksen. Bigger added the extras. That was after Bevan had ruled out a possible try for number eight Tyler Ardron.
Six minutes before half-time Ospreys were awarded a dubious try for prop Dmitri Arhip who emerged from a pile of bodies following a drive from a line-out.
But Scarlets had the last say of the half when Steven Shingler converted a penalty from in front of the posts to cut Ospreys lead to 17-9 at the break.
The Scarlets came out with real intent in the second half and continued to have more than an edge in the scrum.
And a penalty from a scrum allowed Steven Shingler to reduce the Ospreys lead to five points on 57 minutes.
And the former London Irish number 10 was on target again in the 67th minute after Wales hooker Scott Baldwin was caught handling in a ruck.
At that stage Scarlets looked like they had the momentum to go on and seal victory but Ospreys managed to hold out during a frenetic final 10 minutes.