The Blues put one over on the Ospreys in last night's penultimate pool game in the WRU Regional under 18 Championship at Jenner Park in Barry.
However, their 25-22 success in front of a record attendance for the competition - 1300 - does not affect the overall standings in the table.
In fact with the two sides having performed so well in the opening three months of the season, they will meet once again at the end of next month in the final at Llandovery.
With that game in mind, the Blues were understandably keen to strike a physcological blow. And they achieved that courtesy of tries from captain Jake Thomas, Christian Dacey and Lloyd Williams and three conversions and a long range penalty from Joe Deacon.
They led 15-12 at the interval with high performance manager Gafyn Cooper delighted with another excellent performance.
He said, "It was another great night for the boys. The staging of the game could not have been better and the crowd was far and away the biggest we have played in front us.
"They are a good side and made life really difficult for us, but we held on and Joe Deacon's penalty from half way earned us an excellent win."
In the other game, the Dragons recorded a 34-10 win over the Scarlets at Abertillery Park.
Judgement Day is back at the Millennium Stadium for 2015 with the Welsh Rugby Union (WRU) and Regions confirming today that tickets will cost just £10 per head to see all four of Wales' GUINNESS PRO12 sides in action under one roof.
Battling Cardiff Blues produce a performance of full pride and heart in adversity as they lost out to reigning champions Leinster Rugby in a pulsating Guinness PRO12 encounter at BT Sport Cardiff Arms Park.
Cory Allen scored the only try of the game as Cardiff Blues edged an absorbing and dramatic Welsh derby with Newport Gwent Dragons at Rodney Parade to open 2015 in the Guinness PRO12 with a crucial victory.