The Ospreys made hard work of their 14th straight win over Welsh opposition as Newport Gwent Dragons were defeated 20-10.
Cardiff Blues kept alive their faint hopes of securing a place in next season's new-look European Cup with a 17-13 success over Scarlets.
Inspired by the speed and skill of their back three, the Ospreys beat Munster 45-10 in their RaboDirect PRO12 play-off semi-final.
Cardiff Blues number 8 Robin Copeland and Scarlets full-back Liam Williams have both been handed two-week suspensions for red cards received during Sunday's Pro 12 clash at the Millennium Stadium.
Copeland was sent off for stamping, while Williams received his marching orders after picking up a second yellow card of the game.
Williams' initial offence of committing a dangerous tackle was effectively upgraded to a straight red by the game's citing commissioner.
Both players were handed two-week bans at an independent hearing, meaning they are ineligible until midnight on Sunday May 4th.
The Ospreys have triumphed against the Dragons this evening in the second of the 'Judgement Day' derbies.
Final score: Dragons 10 - 20 Ospreys, with tries by Richie Rees and Tom Habberfield.
It's Dragons 0-0 Ospreys at half-time in the second of the 'Judgement Day' derbies. Ospreys's Ryan Jones was given a yellow card for killing the ball.
Judgement Day's first derby has ended Cardiff Blues 17-13 Llanelli Scarlets.
Two yellow cards saw Liam Williams sent off for the Scarlets and a straight red for the Blues's Robin Copeland saw him sent to the stands, leaving both teams down to 14 men in the second half.
It's a second yellow for @sanjaywills and a red for Copeland. Both teams down to 14 men at 55 minutes.
Alex Cuthbert's try and nine points from Gareth Davies's boot have given Cardiff Blues the lead against the Scarlets at half time in the first derby of the day. Rhys Priestland gave the Scarlets their first half points on the scoreboard. Half time - Cardiff Blues 14-8 Llanelli Scarlets.
One of the biggest fixtures in the Welsh regional rugby calendar kicks off later, as 'Judgement Day II' sees the Cardiff Blues take on the Scarlets and Newport Gwent Dragons face the Ospreys at the Millennium Stadium.
With the RaboDirect PRO12 season finale edging closer and both European seeding and derby pride at stake, there is plenty riding on the two contests at the home of Welsh rugby.
The day kicks off at 2pm with 9th placed Cardiff Blues against the Scarlets, who lie three places above them in the PRO12 table in 6th.
The Blues have triumphed in their last two PRO12 matches but have failed to win three in a row since November 2011.
The Scarlets have won on both of their previous visits to the Millennium Stadium, beating Bath in the Anglo-Welsh semi-final in 2006, before emerging victorious against the Dragons in last season's 'Judgement Day' double header.
In the day's second fixture at 4.45pm, Newport Gwent Dragons, who lie 10th in the PRO12 table, take on the Ospreys - the highest placed Welsh region in 5th.
The Dragons are without a win in their last five matches since their defeat to Glasgow at Rodney Parade in February.
As for the Ospreys, they are enjoying better form going into today's contest having won two of their last three matches. They have also been victorious in their last 13 PRO12 encounters against fellow Welsh regions.
The Dragons lost their home RaboDirect Pro12 match to Edinburgh this evening. Tries by prop Willem Nel and centre Matt Scott gave the visitors a commanding lead.
Ross Wardle's late score wasn't enough to save the day for the Dragons.
The Scarlets have withstood a late Connacht fightback to get a bonus point win in the Pro12 this afternoon. Tries from Jonathan Davies and Josh Turnbull, and two touchdowns from Gareth Davies and helped seal the victory.