Campbell College qualified for a Danske Bank Schools' Medallion Shield quarter-final against Sullivan Upper after a 10-5 victory over crosstown rivals Methodist College.
And former Methody pupil Nicholai Koplewski played a bit part in the deciding try at Belmont.
There was only the one score in the first period when the visitors, took the lead following a line-out and drive with a mass of forwards crashing over.
After the restart Campbell's pressure eventually told when left winger Josh Haslett was justly rewarded with an excellent try.
The winning score came after a break from Paddy Beverland, the out-half linking with Koplewski who brought play close to the Methody line before being tackled.
In the process he off-loaded to the promising third form second row Matthew Crowther who went under the posts.
Medallion Shield quarter-finals: RBAI v Ballyclare HS, Coleraine AI v BRA or Rainey Endowed, Campbell College or Methodist College v Sullivan, Wallace HS, Omagh Academy or Dromore High v Ballymena Academy
Medallion Plate quarter-finals: Down HS v Portadown Senior HS, BRA or Rainey Endowed v Wallace HS, Omagh Academy or Dromore High, Bangor GS v Regent House, Portora RS v Campbell College or Methodist College
Medallion Trophy quarter-finals: Ballyclare Secondary v Lurgan College, Dalriada v Downshire, Friends v Foyle & Londonderry or Banbridge Academy, Wellington College v RS Dungannon.