Old Belvedere and Blackrock College shared out five tries in their derby clash at Anglesea Road.
With tries from back-line trio Gary Brown, Alan Henry and Kyle Tonetti, Blackrock edged what was an entertaining tussle.
Leinster man Brown, playing at outside centre, scorched over for the opener and the visitors led 10-3 at half-time.
A Jonathan Slattery try closed the gap to 15-10 but with Tonetti scoring on the hour mark, Richie Leyden's late try was only enough for a losing bonus point for Belvo.
