Prop Duncan Jones replaces Paul James but the hosts are without Wales pair Lee Byrne (thumb) and Shane Williams (Shoulder) for the sell-out showdown.

Captain Matthew Rees returns from a groin injury to lead the Scarlets.

Wales team-mate centre Jonathan Davies and Aussie back-rower David Lyons come back from ankle and shoulder injuries to take their place on the bench.

Scott Johnson's Ospreys bid to extend their winning run against their nearest neighbours to six games in the Boxing Day sell-out.

The two Welsh regions prepare for their Boxing Day bonanza following positive results in the Heineken Cup as both are hopeful of qualifying for the knock-out stages in Europe.

And Ospreys' pack was universally praised following their powerful demolition of Irish giants Munster in the Heineken Cup while their front row was hailed as "one of the best in Europe."

But Johnson has called in Wales loose-head Duncan Jones and dropped James to the replacements bench for their clash with their closest rivals.

The Scarlets are second in the Magners League and have won four of their last five away games while the fourth-placed Ospreys have lost just once at home this term - also against Welsh rivals in a 21-16 defeat by the Dragons.

So as the Magners League top two try-scorers collide, Ospreys coach Sean Holley admits the Scarlets are the "form team."

"They are on fire in terms of their attacking game," said Holley.

"They have young talent full of exuberance and they are going to come up against a pretty physical and determined Ospreys outfit who have a very proud home record.

"It will be a clash of two form Welsh team and it will be a real cracker and this time of year brings out the best in both the fans and players alike so we can expect a good contest.

"I know we have enjoyed the upper hand in recent games against them but the Scarlets are playing well, with a lot of confidence, bringing some players through are in a rich vein of form and scoring a lot of tries.

"The Scarlets always challenge us at the Liberty Stadium and raise their game to play us so with a 20,000 full house it should be a great occasion."

The Magners League champions, who have lost just one of their last seven league games, have only lost twice at the Liberty Stadium to the Scarlets.

But the Llanelli region are without Wales internationals fly-half Stephen Jones (knee) and wing George North (shoulder) as well as their three frontline tight-head props.

Peter Edwards, Deacon Manu (both broken arms) and Rhys Thomas (broken leg) are out as is wing Andy Fenby (groin), second row Lou Reed (leg) and flanker Dafydd Jones (shoulder).

"With the current number of internationals in their squad and the fact they are playing at home will make them firm favourites," said Scarlets coach Nigel Davies.

"But I think that is irrelevant in a local derby."

The sub-plot to this local derby is the personal duels between international rivals as Wales' number one hooker Rees is set to go toe-to-toe with his Welsh deputy Richard Hibbard.

And Dan Biggar and Rhys Priestland will go head-to-head in the battle of number tens that are next in line to Wales regular Stephen Jones.

Ospreys: Barry Davies; Nikki Walker; Tommy Bowe, James Hook; Richard Fussell; Dan Biggar, Mike Phillips; Duncan Jones, Richard Hibbard, Adam Jones, Ryan Jones, Alun Wyn Jones, Jerry Collins, Marty Holah, Jonathan Thomas
Replacements: Huw Bennett, Paul James, Craig Mitchell, Ian Evans, Justin Tipuric, Jamie Nutbrown, Andrew Bishop, Sonny Parker

Scarlets: Dan Newton; Morgan Stoddart; Gareth Maule, Regan King; Sean Lamont; Rhys Priestland, Martin Roberts; Iestyn Thomas, Matthew Rees (c), Simon Gardiner, Jonny Fa'amatuainu, Dominic Day, John Turnbull, Jonathan Edwards, Ben Morgan
Replacements: Ken Owens Rhodri Jones, Phil John, Rob McCusker, David Lyons, Tavis Knoyle, Jonathan Davies, Lee Williams

Referee: James Jones (WRU).

Rugby World cup 2011 match dates

pools A

pools B

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pools D