Ospreys (3) 20
Tries: Phillips, R Jones Cons: Hook 2 Pens: Hook 2
Scarlets (6) 6
Pens: Priestland 2
Mike Phillips celebrates his try against the Scarlets at Liberty Stadium
Wales scrum-half Mike Phillips made a try-scoring full return from knee surgery as the Ospreys saw off their fierce local rivals at Liberty Stadium.
Phillips had not started a game since March, but was highly impressive. Ryan Jones also went over late on.
James Hook added conversions to both tries and two penalties to ensure the hosts Magners League win.
Scarlets fly-half Rhys Priestland, 21, kicked two first-half penalties to help the visitors lead 6-3 at the break.
Phillips returned having played 30 minutes in the Ospreys' previous encounter, a league defeat at the Dragons.
At the same time Shane Williams was absent with a shoulder injury and the Scarlets rested fly-half Stephen Jones, denying fans the chance of seeing him against Wales rival James Hook.
Jones' place was taken by 21-year-old Rhys Priestland, allowing Morgan Stoddart to come in at full-back following shoulder problems.
The visitors also had Gareth Morris on the wing, the experienced former Neath player plucked from Llandovery to plug gaps caused by injuries.
Phillips' efforts apart, there were notable contributions from team-mates Richard Hibbard's ball-carrying, Gavin Henson's midfield power and deft handling and the athletic lock Alun Wyn Jones.
Prop Phil John continued his recent good form in the tight and loose while young half-backs Martin Roberts and Priestland were lively, as was Stoddart.
Priestland had an early impact, kicking the visitors into a 6-0 lead with penalties in the third and fifth minutes.
Hook failed with his first shot at goal after 18 minutes, but put his side on the scoreboard in the 23rd.
Then, in quick succession, referee Nigel Owens sin-binned Stoddart and home skipper Ryan Jones, each of them for killing the ball at the breakdown.
The banishments hurt the hosts more than the visitors as the Scarlets were able to apply pressure up front in his absence.
But Nigel Davies' side were unable to take advantage of their opportunities at that stage. There were also frustrations for the Ospreys, Hook missing a long-range penalty attempt in the 39th minute and knocking on six minutes after the break, denying blood-replacement flanker Marty Holah a score.
However, the frustration ended for the Ospreys in the 56th-minute when Phillips signalled his return, dummying past Morris to break clear from a ruck inside the Scarlets' 22 and score.
That was the only mistake Morris had made on his return to top-flight action, but it proved costly.
Hook converted Phillips, but failed with another penalty before putting his side a converted try ahead in the 68th minute.
Referee Nigel Owens also made an entertaining contribution at one stage, advising Scarlets scrum-half Roberts to desist from trying to influence his decisions.
"I will never make a scrum-half. You will never make a referee - keep to your job," barked Owens.
Ospreys coach Sean Holley:
"It was clear there was only one side who was playing positive rugby and that was the Ospreys.
"In the end there was only one team in it. We got our just rewards for playing positive, attacking rugby, which we were determined to do because there is a full house and we want people to come back and watch us playing attacking stuff."
"That's not a criticism of the Scarlets. I'm applauding the Ospreys for going at it in a local derby in a positive way and playing a real good brand of rugby. In the end you should really say there was only one team in it."
Scarlets coach Nigel Davies:
"I'm not satisfied with the result because I felt we should have had something out of it at the end.
"But I'm very pleased about the way the boys went about their business. I thought they showed a lot of passion and a lot of desire.
"We were up against a team full of quality and I suppose that took its toll in the end.
"But as far as the effort and commitment shown by those players in a Scarlet jersey I'm more than happy. They should be proud of what they have achieved because it's never an easy place to come."
Ospreys: Byrne; Bowe, Parker, Henson, Vaughton; Hook, M Phillips; James, Hibbard, A Jones, A W Jones, Thomas, R Jones, Tandy, Tiatia.
Replacements: Nutbrown for M Phillips (76), Holah for Tandy (46).
Not Used: Shervington, Griffiths, Gough, Biggar, A. Bishop.
Scarlets: Stoddart; Morris, King, Davies, M Jones; Priestland, Roberts; John, Schwalger, Manu, Reed, Maling, Cooper, Edwards, Lyons.
Replacements: Owen for Schwalger (55), Cross for Manu (63), D Jones for Reed (41), Turnbull for Maling (80), Day for Cooper (50).
Not Used: Cattle, C Thomas.
Ref: Nigel Owens (WRU).