Wales prop Samson Lee scored his first try in more than 100 appearances for Scarlets to edge the reigning Guinness PRO12 champions to victory over arch-rivals Ospreys.
Dan Biggar punished the stream of breakdown penalties awarded against the champions to keep the home side in the fight at Liberty Stadium.
But not even his perfect six from six was enough to haul them over the line in the end as Gareth Davies crossed twice for the visitors in a 19-18 away success.
It meant a fifth successive PRO14 defeat for the four-time former champions to deepen their crisis and leave them anchored to the bottom of Conference A.
Victory for Scarlets took them back to the top of Conference B and put them in good heart ahead of their tough trip to Toulon in the European Champions Cup next weekend.
The visitors showed off their firepower in the opening few minutes when Johnny McNicholl and Rhys Patchell combined to send Davies scampering for the right corner from 40 metres out.
Cory Allen managed to stop him in the corner on that occasion - but there was no catching the Welsh scrum-half in the second half.
Davies ran in two tries after Steffan Evans and then Hadleigh Parkes opened up the home defence to give him a clear run to the line. His second try allowed the champions to level the scores on 50 minutes after Biggar's boot had given the Ospreys a 9-0 lead.
Biggar's fourth penalty success came in between the two Davies tries and his fifth made it 15-12 six minutes later.
However, Scarlets were in no mood to be denied and their second-half performance was full of the tempo that was missing from the opening 40 minutes.
Lee's try came from a driving line-out moments after Wyn Jones had had an effort ruled out and Dmitri Arhip had been sent to the sin-bin. This time Patchell hit the mark with a wide angled conversion.