The relative ease with which Waterford dominated the game virtually from the start begged the question as to how a replay of this FAI Cup second-round tie was needed at all.
Having struggled to put away the first division's bottom side at the RSC on Friday night, Waterford never looked in danger this time as goals late in each half from Paul Scully and Alan Kirby confirmed their visit to Belfield for a third-round meeting with UCD.
Having come close on two occasions through Kevin Waters, the first goal came after 31 minutes. John Frost's ball forward was skilfully controlled by Aaron Moroney who sent Paul Scully in behind the home defence. Scully did the rest, drawing Gary Rogers off his line before finding the corner of the net.
Right back Martin Francis twice came close early in the second half for the home side before their cause was dealt perhaps a fatal blow with Graham Doyle's sending-off for a second bookable offence in the 56th minute.
Kirby then missed two openings before adding Waterford's second goal on 73 minutes, sidefooting home Dave Whittle's cross.
St Francis finished with nine men as John Chandler was also ordered off for a second bookable offence a minute from time by Dublin referee David McKeon, who issued a total of 12 bookings during a game that was never overly physical.
St Francis: Rogers; Reid, Fitzell, C Tighe; Francis, Doyle, Chandler, Richard, Foxton; O Tighe, Stokes. Subs: Kelly for O Tighe (62 mins), McDonagh for Foxton (77 mins).
Waterford United: Fennelly; D Whittle, Breen, Rea, Frost; Kirby, K Whittle, Reynolds, Waters; P Scully, Moroney. Subs: Bradley for Moroney (65 mins), O'Brien for D Whittle (80 mins), A Scully for P Scully (85 mins).
Referee: D McKeon (Dublin).