Cardiff Blues North U18 picked up a losing bonus point following a 24-19 defeat to Ospreys at Sardis Road on Wednesday.
The hosts battled back to take the lead, following a 17-7 half time deficit, but were dealt a blow as Ospreys crossed for a decisive score with 10 minutes remaining.
Both sides were reduced to 13 men after tempers flared during the second half.
It only took 15 second for the visitors to open the scoring as a break and offload from Frankie Jones paved the way for number eight Will Barraclough to cross the whitewash.
The conversion was wide, but Cardiff Blues North replied instantly, as wing Liam Lloyd touched down, with Rhys Davies' conversion pushing the hosts ahead.
With 23 minutes on the clock, Barraclough edged his side back ahead with his second score of the evening, before a Bradley Roderick try saw the Ospreys head in at the break with some breathing space, making it 17-7.
Cardiff Blues North wing George Thomas made instant impact in the second half, as his try, followed by another Davies conversion, narrowed the visitors' lead to 17-14, before flanker Callun James completed the comeback with a try five minutes later.
Davies was off-target with his conversion attempt this time, but both sides were soon reduced to 13 men as tempers flared following a tackle from Ospreys' Iwan Shenton.
The aftermath of the tackle resulted in Shenton and Garin Lloyd shown red cards for the visitors, alongside Cardiff Blues North's Garyn Phillips and Thomas John.
Ospreys would go on to secure the win and a bonus point as Ben Cambo scored a decisive try with just over 10 minutes remaining on the clock.