The North Tipp School fought back from 14 points to 5 down and scored a late try in the game's final few minutes to secure the victory.
Their Coach Pieter Swanepoel said his side are no longer just competing, they are winning.
He said: https://soundcloud.com/tippfmradio/coach-pieter-swanepoel-on-his-sides-win-over-blackrock
The full-time score in Donnybrook was Blackrock 14 Cistercian College Roscrea 17.
Roscrea join Clongowes and Newbridge in the semi-finals, meaning three non-Dublin teams in the final four.
The last of the quarter-finals between Monkstown and Belvedere, takes place on tomorrow.
Elsewhere, the draw for the semi-finals of the Munster Senior Schools Cup will see Rockwell College cup against Limerick side Glenstal.
The Tipp School saw off the challenge of St Munchins in Clanwilliam earlier this week.
And the other semi-final has Ardscoil Rís up against Presentation Brothers College of Cork.
