Ospreys (3) 28 Tries: R Jones, S Williams, Byrne. Cons: Hook 2. Pens: Biggar 2, Hook.
Ospreys wing Shane Williams takes on Scarlets full-back Daniel Evans
Ospreys earned the bragging rights over Scarlets after coming from behind in a west Wales derby that was often fractured and occasionally fractious.
Trailing 12-3 at the break to four Rhys Priestland kicks, Ospreys hit back with their Lions candidates to the fore.
Ryan Jones started the recovery, Shane Williams added a second try, before a James Hook break sent Lee Byrne - back after injury - away under the posts.
That onslaught reduced Jon Davies' try to a consolation score for Scarlets.
The west Wales derby attracted an encouragingly large crowd at a Parc y Scarlets bathed in early evening spring sunshine.
One of those watching was Scott Johnson, the former Wales caretaker and skills coach who arrived back in Wales on Friday and will soon take over as Ospreys' new director of rugby.
Scarlets' move to their new stadium has coincided in a slump in form that has delivered scarce entertainment and few wins to attract the crowds.
But 11,444 were on hand to see the Ospreys pack take an early grip and probe deep into Scarlets territory with a series of drives that drew an early penalty.
Dan Biggar put the visitors into the lead but Scarlets were level soon after as Priestland punched through a huge kick from almost on the halfway line.
Priestland had been handed the fly-half shirt and kicking duties due to Wales pivot Stephen Jones withdrawing just before kick-off with a hamstring strain.
The Scarlets had had to reshuffle their backline further as centre Gavin Evans also withdrew at the last moment with a tweaked calf muscle.
Despite those pre-match set-backs it was Scarlets who settled better and they nearly took the lead when Davies charged down a Mike Phillips kick, only to knock-on as he tried to gather the loose ball.
An out-of-sorts Ospreys rarely threatened for the remainder of a fractious and grumpy first half, allowing Priestland to chip the Scarlets into a 12-3 lead with three more penalties from four attempts.
In truth the most eye-catching moments from the first 40 minutes were when the simmering rivalry between the two sides broke out into open conflict.
An early break down the right wing from Phillips - Davies doing well to tackle him into touch - heralded a better half and Ospreys soon claimed the game's first try.
Biggar gave the ball air to make use of numbers and skipper Ryan Jones went over at the left corner flag for an unconverted try, although Biggar did add a later penalty.
With the Lions squad due to be named on Tuesday there was a welcome return to action after injury for Ospreys full-back Byrne, who replaced Gareth Owen, while James Hook was a half-time change for Sonny Parker.
The rustiness was evident as Byrne's first attempted clearance was charged down by Rob Higgett, although the ball bounced safely into touch.
Having seen their lead cut to 12-11, Scarlets hit back thanks to some individual brilliance from Daniel Evans.
The full-back gathered his own up-and-under from Ospreys wing Tommy Bowe and set the ball back for Davies to go over for seven points.
Ospreys sent on their big guns, with Adam Jones and Alun Wyn Jones coming off the bench to bolster the pack.
The reinforcements paid dividends in terms of possession and territory, but between them Hook and Biggar were profligate with their goal-kicking and their was no scoreboard reward.
However, Scarlets lost prop Deacon Manu to the sin-bin on 62 minutes for some foolishness at a ruck and Ospreys took control.
From turnover ball Phillips raced away down the left wing and sent Williams over the line with an inside pass, Hook at last landing a kick with the conversion.
Then Hook produced a scorching midfield break that allowed Byrne, shaking off some of that rust with a brilliant supporting run, to go under the posts.
Hook's conversion and a late penalty made the win safe at 28-19, although Priestland missed a late kick that would have brought the Scarlets within seven points for a losing bonus point.
Scarlets coach Nigel Davies: "The yellow-carding [of prop Deacon Manu] was obviously a key moment in that game, which was a very tight and intense encounter.
"We know statistically that once a guy goes off the field the opposition scores points and I think there were 14 points scored in that period.
"We had a couple of late changes that we had to make and I'm delighted really with the way that the boys have stood up to it."
Scarlets: Daniel Evans; Mark Jones, Jon Davies, Rob Higgitt, Lee Williams; Rhys Priestland, Martin Roberts; Phil John, Matthew Rees, Deacon Manu, Vernon Cooper, Dominic Day, Josh Turnbull, Dafydd Jones, David Lyons. Replacements: Iestyn Thomas, Mahonri Schwalger, Aaron Shingler, Rob McCusker, Gavin Cattle, Nick Reynolds, Ifan Evans.
Ospreys: Gareth Owen; Tommy Bowe, Sonny Parker, Jonathan Spratt, Shane Williams; Dan Biggar, Mike Phillips; Paul James, Richard Hibbard, Cai Griffiths, Filipo Levi, Andy Lloyd, Tom Smith, Marty Holah, Ryan Jones (capt). Replacements: Huw Bennett, Adam Jones, Alun Wyn Jones, Steve Tandy, Rhys Webb, James Hook, Lee Byrne.
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