Holders Roscrea have qualified for the Leinster Senior Cup final.
They did it the hard way by storming back from a 10-0 deficit to full-back Michael Silvester's try and five points from centre Benjamin O'Shea by the 17th minute.
The maul was their main method of transport as they halved the lead with prop Dylan Murphy's try which was answered by O'Shea's second penalty for 13-5 to Clongowes at the break.
The Clane school just couldn't put enough on the scoreboard to take them away, prop Michael Milne driving over for his first try for full-back Conor Kelly to make it 13-12 in the 49th minute.
It was then Clongowes wrestled back control by moving the ball into the wide channel where wing Fiachra Lynch finished in style.
They did not score again as Roscrea came on strong, mainly through their forward pack, to set up tries for Milne and flanker Brian Diffley, the second converted by Kelly.
They held out to make it through to the final where they will meet the winners of Belvedere and St Michael's tomorrow.
schools: Roscrea 24 Clongowes 18