Mike Phillips celebrated his first start for nine months by scoring a try in the Ospreys' Magners League derby win over the Scarlets in front of a capacity crowd of 20,520 at the Liberty Stadium.
The Wales scrum-half, who had surgery on his knee ligaments in March, crossed on the hour mark after the home side had trailed 6-3 at half-time. A second try for Wales captain Ryan Jones five minutes into injury time denied the Scarlets a losing bonus point.
The Ospreys were without Shane Williams, sidelined with a shoulder problem. The visiting Scarlets were also without three of their big-name stars - Stephen Jones and club captain Simon Easterby were rested while hooker Matthew Rees had a shoulder problem.
After a frenetic start the Scarlets opened the scoring in the third minute with a Rhys Priestland penalty after the Ospreys had erred offside. The Scarlets doubled their lead seven minutes later with a second Priestland penalty.
The Ospreys spurned the best tryscoring chance of the first period when Gavin Henson broke clear of the Scarlets defence and on 30 minutes James Hook was off-target with a penalty.
Hook found his range minutes later, planting a penalty after Mark Jones and Regan King had collided trying to collect a Priestland cross-kick. The Scarlets and Ospreys both suffered setbacks when Morgan Stoddart and Ryan Jones were both yellow-carded for not releasing the ball on the floor. In first-half injury time Hook spurned a chance to level the scores, missing a penalty from close to his halfway line.
Seven minutes into the second half blood replacement Marty Holah crossed the line but the score was ruled out for a knock-on by Hook. On the hour mark Phillips skipped past two would-be tacklers to slide in under the posts for a converted try to give the Ospreys a 10-6 lead.
As the match entered its last 10 minutes Hook planted his second penalty to extend the Ospreys' advantage before Jones went in under the posts for the second converted try.
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.
Att: 20,520
Ref: Nigel Owens (WRU)