Cory Allen, Harry Robinson (2), Owen Rees (2) and Ryan Evans all crossed for the Blues with outside half Rhys Patchell adding three conversions and Garin Thomas one. Patchell also kicked a penalty while for the Ospreys, Nicky Davies scored their lone try and Sam Davies converted. Among the interested spectators at the game were Blues director of rugby Dai Young, Scarlets coach Nigel Davies, father of Ospreys' outside half Sam and Ospreys' director of rugby Andrew Hore.
Having lost out to the Scarlets, 15-13, the oprevious week, the Blues are back on course to reach the final with Young particularly delighted with the next wave of players coming through.
"There were some good players out there, on both sides, to win by that margin is obviously an excellent result for the boys," said Young.
Down the road at Newbridge, the Dragons came close to ending the Scarlets unbeaten record - eventually going down 26-20 to a side inspired, once more, by outside half Jordan Williams.
Having scored 36 points in his side's opening two victories, over the Ospreys and Blues, Williams helped himself to another 21 as the visitors edged out a combative Dragons side.
Williams scored a try and kicked a conversion and four penalties while replacement scrum half Rhodri Williams added a second try for good measure. For the Dragons, who trailed 13-8 at the interval, there were tries from Dominic Franchi, after 10 minutes, Elliot Dee after 44 and replacement hooker Jack Williams 10 minutes from time. Ethan Davies kicked a penalty and a conversion, but it was not enough to deny the Scarlets a third successive win of the season.
There is seemingly no stopping the Ospreys under 16s who not only took the North's unbeaten record, but in doing so, maintained their own with a fourth successive victory of the season, at Llandarcy Academy.
However, the hosts left it desperately late with Liam Popham helping his side to a 10-8 victory with a try three minutes from time.
Outside half Josh White, who had earlier kicked a penalty, converted from the touchline and the Ospreys managed to hold out for the final few, heart-stopping moments.
Jarrod Evans' 25th minute penalty provided the North with the advantage and when scrum half Shaun Clarke muscled his way in for an unconverted try shortly after half time, the visitors looked well set for a fourth successive victory of the campaign, and a first away from their home base at Abercwmboi.
However, it was the Ospreys who came out on top thanks to the latye intervention of Popham and White and some sterling defence in the final seconds when the North were camped out on the Ospreys' line.
There was equal joy at Parc y Scarlets where the Scarlets under 16s managed a first win of the season, 14-7 against the Dragons. A try from Ashton Hewitt, converted by Lloyd Rogers put the Dragons in front during the first quarter, but by half time, the hosts were level courtesy of a try from scrum half Gareth James and a conversion from Jack Maynard.
The issue was settled a minute into the second half when Bradley Davies was driven over for a try that Maynard improved.