Newport Gwent Dragons claimed just their second away win over Cardiff since the
inception of regional rugby at a packed Arms Park.
Leinster travel to Munster, Ulster host Connacht and Cardiff Blues take on Newport Gwent Dragons on Boxing Day.
Cardiff Blues lock Teofilo Paulo and Scarlets forward Joe Snyman have been cited for foul play.
Watch all the highlights of this weekend's Guinness PRO12 action.
Exeter have confirmed Tom James will head back to former club Cardiff Blues at the end of the season.
Josh Navidi helped Cardiff Blues draw first blood in the festive Welsh derby season after a 21-9 defeat of Scarlets.
Team news for Friday's Pro12 clash between Cardiff Blues and Scarlets at the Cardiff Arms Park.
Saturday proved to be a Premiership party in the Challenge Cup, with wins for Exeter, London Irish and Gloucester.
Round Four of the European Rugby Challenge Cup continues on Saturday, with six fixtures on the cards.
Wins for Cardiff Blues, Connacht and Newport Gwent Dragons in round three of the European Challenge Cup.
Saturday's European Rugby Challenge Cup billing sees four matches, with London Irish and Connacht both in action.
Cardiff Blues beat Treviso to secure their second PRO12 win of the season but were hit by an injury to Gareth Anscombe.
Gloucester back Tom Isaacs has left the club with immediate effect and joined the Cardiff Blues.
Third-placed Munster will be looking for revenge against second-spot Ulster in the PRO12 on Friday night.
Edinburgh posted their third win of the Guinness PRO12 campaign as they saw off Cardiff Blues 28-13 at Murrayfield.
Leinster welcome back Jordi Murphy and Dave Kearney for the weekend trip to Treviso, which is live on Sky Sports 2 HD.
Cardiff Blues have signed Argentina utility back Joaquin Tuculet until the end of the season.
Cardiff Blues are in a strong position to progress in the LV= Cup after a 19-13 triumph over Welsh rivals Scarlets.
Cardiff Blues academy manager Richard Hodges hailed the hard-fought nature of their 19-13 LV= Cup win over the Scarlets.
Four Welsh teams are in action on Friday in the second round of LV= Cup action.
The biggest and toughest hits and tackles plus the best tries from the world of rugby union.