A fast start which saw CBS Naas 10 points to the good after seven minutes was the bedrock of their win over St Patrick's Navan at Ashbourne RFC.
Second-row Mike Russell went over in the second minute, with fly-half John O'Brien converting and adding a penalty five minutes later.
St Pat's out-half Cillian Farrell reduced the gap with a penalty, only for Naas wing Daniel Devlin to beat three defenders from the 10-metre line for the Kildare school's second try in the 20th minute.
St Pat's shaved the deficit to 15-10 with a try under the posts by openside Conor Farrell, converted by his brother Cillian.
A litany of mistakes made headway difficult for both sides in the second period, but Naas No 8 Rian Pearse eventually swiped a try, with O'Brien converting.
CBS Naas – D Murphy; D Watson, C Fitzsimons, L Mather, D Devlin; J O'Brien, D McGrath (capt); A Coyle, L McCormack, S Lackey, C Gorry, M Russell, D Nugent, S Nolan, R Pearse.
St Patrick's – T Hamilton (M Dunne h-t); J Ntambwe, A Keating, H Hester, M Melvin (M Blachowski 60); Cillian Farrell (capt); J Shealy (C Bled 60); C Stafford (J Deane 64), D Meegan, E McGrane, R Scott, B Gore, R Meegan, Conor Farrell, S Faulkner.
Ref – J Fegan (Leinster Branch).