BILLY O'HORA scored a stunning late try to seal victory as Crescent CC finished with a flourish at the Mardyke.
With the game approaching the 60-minute mark, the Limerick side led 8-5 when Pres were awarded a penalty, but Barry Ryan's effort was short.
In their next attack, Crescent's Cian Clifford landed a second penalty and then, deep in injury-time, O'Hora made a knifing run from halfway before touching down to make sure of victory.
Jack Lyons' penalty had put Crescent ahead, but lock Luke O'Connor went over in the corner for Pres after sustained pressure.
Shortly before half-time, Glen Dickinson restored Crescent's lead following a fine Calvin Nash break, and while Conor Slattery was sin-binned early in the second half, Pres could not take advantage.
CRESCENT CC – G Dickinson ( L O'Connell 41-43); C McSweeney, B O'Hora, C Nash, J Young O'Connor ( L O'Connell 55); C Clifford, J Lyons; A Thai, J Barry, S Scanlon Garry; B Considine, J Blake; C Slattery, P Hickey, N Mulcahy.
PBC – P Fitzgerald; S O'Brien (J Costello 49), S Lucey, R Murphy (K O'Leary 40), C Duggan (J Costello 29-30); B Ryan, B Pope; C Ormond, M Shinkwin, S Deane; F Kelleher, L O'Connor; G Smith, E O'Shea, B O'Mahony.
Ref – C Harrington (MAR).