However, a first half Biggar penalty, a try from Alex Stubbs and then Biggar's last gasp strike left the Blues with only a bonus point for their efforts.
Gafyn Cooper Regional Performance Manager commented,
'I really feel for the players and management after we dominated for long periods. The players have to learn from this defeat and bounce back as better players'.
Ospreys U16 11pts Cardiff Blues South 9 pts
Meanwhile, having failed to make any impression at any age group last season, the Dragons under 16s are bang on course to reach a first WRU Reebok final thanks to a 17-8 victory at the Scarlets.
David Jones put the Dragons on course with a try after 13 minutes - a quickly taken tap penalty catching out the Scarlets - and Adam Hughes' conversion and 23rd minute penalty helped the visitors into a 10-8 interval lead.
However, thanks to a resilient performance in the second half and a 61st minute try from Aaron Coundley, once again improved by Hughes, the Dragons took the points and enhanced their lofty position.
The victory leaves the Dragons seven points clear of the Blues North and six points ahead of the South.