Ben Murphy's try for Pres condemned last year's beaten finalists St Munchin's to defeat at Corbally.
PBC won because they made fewer mistakes and their scrum dominated, forcing a series of penalties.
In addition, the Cork school had the best player on view in scrum-half John Poland, who provided fluent service and also kicked two penalties.
PBC missed a penalty after four minutes before they changed kicker and Poland opened the scoring after 20 minutes. Munchin's drew level 10 minutes into the second half, but after 52 minutes came the only try.
Munchin's full-back Shane Halpin attempted to trap a kick with his foot. But the ball spun upwards and into the hands of winger Murray, who raced more than 30 metres to touch down.
Poland was inches wide with the conversion, but then landed an insurance penalty.
PBC – J Daly; R Reardon (C Flanagan 65), P O'Brien, C Murphy, B Murphy; P Kiernan, J Poland; M Curtin, M Abbott, S MacCarthy; D Lane, C Casey; M Carey, D St Leger, M Murphy.
St Munchin's – S Halpin; K Faloon (S Doona 50), D Goggin, E O'Keeffe, G Bateman (D Kelly 52); S Airey, R Meagher; D Begley, J Prenderville, B Keogh (E Brennan 47); S O'Mullan, K Browne (T O'Dwyer 42); L Nicholas, J Sheehan, B Kilkenny.
Ref – K Imbusch (MAR).