In the under 18s the Scarlets and Ospreys missed out on a chance of leap-frogging the Blues as they shared 30 points at Parc y Scarlets.
Victory for the Blues North in North Wales on Sunday meant the Ospreys under 16s needed to win with a bonus point to regain pole position. And they achieved that courtesy of a try hat-trick from wing Dafydd Howells.
Howells, who now has nine tries for the season, and scrum half Daniel Brooks both crossed twice in a first half that saw outside half Josh White add three conversions as the hosts led 26-13 at the interval. Howells completed his hat-trick on the hour before two tries from Steffan Evans and as many conversions from Jack Maynard made sure of a losing bonus point for the Scarlets. Maynard converted a penalty try in the first half and added a penalty while Jamie Evans slotted a long range penalty as the Scarlets went down 33-27.
The Dragons, who were 20-16 winners against Blues South at Cross Keys in August, completed the double over their neighbours thanks to tries from Ashton Hewitt (2), Hallam Amos and Jack Dixon. Outside half Lloyd Rogers kicked two conversions in his side's 24-0 victory at Rumney.
Dragons flanker Rhys Pugsley and Blues' lock Michael Snook were both yellow carded.
Victory keeps the Dragons in third, eight points clear of the Scarlets and a further five points ahead of Blues South for whom qualification looks highly unlikely.
Locked together at 5-5 at half time, the Scarlets and Ospreys' under 18s drew 15-15 with the hosts recovering from a 15-8 deficit to snatch a share of the spoils. Hooker Evan Yardley helped himself to a try, as did Ben Roberts, while Sam Davies added a conversion and penalty for the Ospreys. Steffan Hughes crossed twice for the Scarlets with leading scorer Jordan Williams kicking a conversion and penalty.