We look at Wednesday's fixtures
Round 12 of the Pro12 competition kicks off on December 26 with two Welsh festive derbies.
Second-placed Scarlets travel to Swansea to play Ospreys at the Liberty Stadium, whilst over in the east Cardiff Blues welcome Newport Gwent Dragons to the Arms Park.
If Ospreys are to retain their title they need to start pushing for a play-off spot, but currently find themselves five points short of the cut-off - with a game in hand as their Round 11 fixture against Dragons has been held over until December 31st.
Cardiff Blues are on the wrong end of a run of losses, and need a victory to boost this season's campaign.
The Scarlets travel to the Ospreys on Boxing Day for the second of their big Welsh derby fixtures boosted by a win on the road at the Arms Park and tightening their grip on their top two position in the Pro12.
One of the biggest contests and most eagerly anticipated games of the season for supporters in the West, the traditional Boxing Day fixture for the Scarlets against their closest rivals never fails to bring added edge and drama.
The Scarlets are facing quick turnaround from their battle last Friday at the Cardiff Blues, while the Ospreys have had more rest time, not having played since their win over Toulouse in the European Cup.
The Scarlets make four personnel changes to the starting line-up that was victorious at the Arms Park with Aled Davies getting a start back at scrum-half; former Osprey Kristian Phillips comes onto the wing, Matthew Rees starts at hooker and Jake Ball comes into the second row alongside George Earle.
The Ospreys host the Scarlets with a strong home record behind them this season having been victorious in their last seven games at Liberty Stadium. The Ospreys have won their last five clashes with fellow Welsh regions.
Scarlets have won five of their last six Pro12 fixtures, the only defeat being against runaway leaders Ulster on 2 December.
The West Wales side will be boosted by their strong form on the road with the Scarlets having won five of their six away fixtures this season in the league - their only away loss in the competition this season was 20-22 at Treviso on 29 September.
Scarlets have won eight of their last nine encounters with fellow Welsh regions. The West Walians last beat Ospreys 22-14 at Parc y Scarlets exactly 12 months ago.
"There's never any need for motivation for coaches or players for this fixture. We may have had less preparation time, but the boys have worked hard on their recovery during the four-day turnaround and they know how significant this game is for us on a number of levels," Scarlets attack coach Mark Jones said.
"It's going to be a very intense game and a typically physical match. We don't have to cast our minds back too far to our last encounter with the Ospreys and where in the game we came out second best.
"We know the quality the Ospreys have, they'll come out strong will be feeling confident after an impressive win over Toulouse in Europe. It's going to be a high impact and a big battle up front but the players are in the right mindset and we're looking forward to a great contest."
Scarlets flyhalf Aled Thomas said: "We adjusted our game last weekend, the forwards carried well and made the hard yards for us and overall we controlled territory well. We'll need to step up again for this encounter, the Ospreys have strength across the field but we if can get quick ball to our backs – we know we have the talent do some damage.
"We want to build on that performance this week; it was difficult in the conditions last Friday to play an expansive game but what mattered was four points and keeping our campaign for a play-off place on track.
"We want to stamp our authority on this game and to keep that place – so there's plenty riding on this fixture for both sides. Wins on the road are what count in this competition if you want to make the play-off places."
Ospreys head coach Steve Tandy said: "This game marks the start of a very busy month for the Ospreys and it's crucial that we perform consistently, putting in top level performances in every single game now so that we can push for a top four spot in the PRO12 and the knockouts in Europe.
"This is the type of game that everybody wants to be involved in so training has been full on this week, which is great when you are a coach. We've got three big games in nine days so the challenge for us is to make sure the team is properly prepared for each one, and that will mean making a few changes along the way to keep people fresh and to give us the best chance of getting the performance levels in that we'll need if we are going to get the result we want from these games.
"After Boxing Day we go to the Dragons and then we play Zebre at the Liberty on 4th January in another crucial home game and we know that we have to be at our very best for each game if we want to move into the top four and stay there.
"With the biggest crowd in two years already confirmed for Boxing Day we know that there's going to be a great atmosphere, which is fantastic. It'll be pretty special, we've got good memories of playing the Scarlets at Christmas at the Liberty and it's up to these boys to make their own history this week.
"We know that they'll come here confident after winning at the Blues last week, they are a very dangerous team so we will have to be at our best if we are going to send our supporters home with the best Christmas present they could ask for."
We look at Wednesday's fixtures!
CARDIFF BLUES v NEWPORT GWENT DRAGONS
(Cardiff Arms Park - Kick-off: 14.05; 14.05 GMT)
Cardiff Blues' only victory in their last seven Pro12 matches was 14-7 against Zebre in Parma on 25 November.
The Blues have won just one of their last seven fixtures in all competitions at the Arms Park: 22-17 versus London Wasps in the Anglo-Welsh Cup on 9 November.
Cardiff Blues have won just one Welsh inter-Regional game since last Christmas: 16-5 at the Dragons on 15 September.
Newport Gwent Dragons have won three of their last four encounters in all tournaments, but have not won away from home in the PRO12 since a trip to Edinburgh on 23 March.
The Dragons have triumphed just once on opposing turf against a fellow Welsh region since 2007: 21-16 at Ospreys on 30 October 2010.
Dragons' solitary win against Blues in Cardiff remains 25-13 on 7 November 2003.
Cardiff Blues: 15 Jason Tovey, 14 Alex Cuthbert, 13 Gavin Evans, 12 Dafydd Hewitt, 11 Harry Robinson, 10 Rhys Patchell, 9 Lewis Jones, 8 Andries Pretorius (captain), 7 Sam Warburton, 6 Robin Copeland, 5 Lou Reed, 4 Bradley Davies, 3 Scott Andrews, 2 Rhys Williams, 1 Sam Hobbs.
Replacements: 16 Kristian Dacey, 17 Taufa'ao Filise, 18 Benoit Bourrust, 19 James Down, 20 Josh Navidi, 21 Alex Walker, 22 Ceri Sweene, 23 Richard Smith.
Newport Gwent Dragons: 15 Hallam Amos, 14 Will Harries, 13 Pat Leach, 12 Andy Tuilagi, 11 Mike Poole, 10 Dan Evans, 9 Wayne Evans, 8 Toby Faletau, 7 Nic Cudd, 6 Lewis Evans (captain), 5 Rob Sidoli, 4 Andrew Coombs, 3 Dan Way, 2 Sam Parry, 1 Phil Price.
Replacements: 16 Hugh Gustafson, 17 Owen Evans, 18 Nathan Buck, 19 Adam Jones, 20 Tom Brown, 21 Jonathan Evans, 22 Lewis Robling, 23 Jack Dixon .
Referee: Leighton Hodges (Wales)
Assistant Referees: Ian Davies, Wayne Davies (both Wales)
TMO: Tony Rowlands (Wales)
OSPREYS v SCARLETS
(Liberty Stadium - Kick-off: 17.30; 17.30 GMT)
Ospreys' last 10 matches in all competitions have all been won by the home side on the day, whilst they have been victorious in their last seven games at Liberty Stadium since Glasgow won there on 14 September.
Ospreys have won their last five clashes with fellow Welsh regions.
Scarlets have lost only one of their last six Pro12 fixtures: 12-19 at home to runaway leaders Ulster on 2 December.
Scarlets' solo away loss in the competition this season was 20-22 at Treviso on 29 September. Scarlets have won eight of their last nine encounters with fellow Welsh regions.
The West Walians have beaten Ospreys only once since 2007: 22-14 at Parc y Scarlets exactly twelve months ago.
Scarlets: 15 Liam Williams, 14 George North, 13 Jonathan Davies (captain), 12 Scott Williams, 11 Kristian Phillips, 10 Aled Thomas, 9 Aled Davies, 8 Kieran Murphy, 7 Aaron Shingler, 6 Josh Turnbull, 5 George Earle, 4 Jake Ball, 3 Samson Lee, 2 Matthew Rees, 1 Phil John.
Replacements: 16 Emyr Phillips, 17 Shaun Hopkins, 18 Jacobie Adriaanse, 19 Sione Timani, 20 Rob McCusker, 21 Tavis Knoyle, 22 Gareth Owen, 23 Gareth Maule.
Ospreys: 15 Richard Fussell, 14 Ross Jones, 13 Andrew Bishop, 12 Ashley Beck, 11 Eli Walker, 10 Dan Biggar, 9 Kahn Fotuali'i (captain), 8 Joe Bearman, 7 Justin Tipuric, 6 Ryan Jones, 5 James King, 4 Ian Gough, 3 Adam Jones, 2 Richard Hibbard, 1 Ryan Bevington.
Replacements: 16 Scott Baldwin, 17 Duncan Jones, 18 Cai Griffiths, 19 Lloyd Peers, 20 Morgan Allen, 21 Rhys Webb, 22 Matthew Morgan, 23 Tom Isaacs.
Referee: Nigel Owens (Wales)
Assistant Referees: Gwyn Morris, Jon Mason (both Wales)
TMO: Derek Bevan (Wales)