The defending league champions are now 13 points behind table toppers Leinster albeit with a game in hand, while this win may just give the Scarlets the confidence to mount a concerted title push in the new year.

Possession wise, the Ospreys were well on top but they were ultimately frustated by the hosts who limited Lyn Jones' men to four penalties from James Hook.

These sides certainly went at it hammer and tongs and in the end, tries from Gavin Thomas (16 minutes) and Nathan Brew (49) settled the tie.

The Ospreys welcomed back their captain this season, Ryan Jones, from a shoulder operation and despite losing scrum half Mike Phillips to a second-minute sin-binning and starting without eight regulars, the visitors took a 9-7 lead into the interval.

The Ospreys' away form - they had won four of their last five games on the road - meant they were always going to be a threat, but it was the Scarlets, beaten twice by Munster in Europe recently, who looked set to take an early lead.

The game was only 90 seconds' old when Phillips saw yellow for tripping the onrushing Mark Jones as he chased a kick through.

Stephen Jones missed the resulting penalty kick - his effort bounced back off the near post - and the Scarlets, despite a lively run from replacement Brew, just could not make the most of their numerical advantage.

The Ospreys went in front in the 14th-minute when Hook nailed a penalty after Scarlets captain Simon Easterby had been pinged for going off his feet at a ruck.

Two minutes later, the Scarlets had the ideal response when Stephen Jones kicked a penalty to the corner, lineout possession was secured and the rampaging Thomas sliced through on the blindside for a well-taken try.

Jones converted and while the Scarlets lost both Gavin Evans and Alix Popham to injury during a fiercely contested 40 minutes, Phil Davies' side remained in front until late in the half.

Hook punished two ruck offences from Vernon Cooper after 30 and 35 minutes to edge the Ospreys in front for the second time. Cooper was sin-binned for the second misdemeanour and the Ospreys almost snuck through for a try before half-time.

An overthrown lineout from Matthew Rees was gobbled up by Ben Lewis, and the Ospreys flanker made 50 metres before the retreating Mark Jones brought him to ground. Had Lewis got his pass away, the supporting Aled Brew look certain to make the line.

The Scarlets defence recovered and the home side regained the lead, eight minutes after the break, when Jones punished Ian Gough for coming in at the side of a ruck.

The Scarlets raced 17-9 clear when turnover ball led to Brew exposing some poor defending from Lee Byrne and Mark Taylor and the replacement had the gas to touch down, with Jones adding the conversion.

Hook cut the gap to five points when fit-again skipper Jones won a penalty on the Scarlets 22 but that was as close as the Ospreys got.

All Black Justin Marshall was sprung from the bench and made an immediate impression. He made an excellent break but was stopped just short of the whitewash by Dafydd James and Mark Jones.

The Ospreys' handling continued to let them down and centre Andrew Bishop managed to knock on with the line in sight. The champions' lineout was also suffering as Cooper secured a number of steals on Huw Bennett's throw.

Wales fly-half Jones missed a 77th-minute penalty for the Scarlets but they duly hung on to complete a season's double over their Welsh rivals - Davies' charges were 14-9 winners when the sides met at Liberty Stadium in September.