Back row Alun Lawrence grabbed a try brace as Cardiff Blues Under-18s remained top of the Regional Age Grade Championship and completed the double over Ospreys Under-18s with a 31-10 win at St Helens on Tuesday night.
The home side took the lead with a try from scrum half Connor Tantum after only four minutes, with Cai Evans adding the extras.
However, after that the Cardiff Blues slowly took control of the fixture - to cement top spot with one round to go against second placed Scarlets next week - with a Lawrence try on 17 minutes converted by Ben Thomas.
Ospreys lost centre Ewan Gully just before the break, when he was yellow carded, and Lawrence grabbed his second of the night moments after the restart to send Cardiff Blues ahead for the first time.
Scrum half Dane Blacker extended the lead to 24-10, with Thomas converting again, before they grabbed a bonus point with a late try from replacement Garyn Payne.