Diarmuid Connolly's side showed their intent from the throw-in, with Clontarf goalkeeper Ross O'Hanlon put under pressure in the second minute with a shot on goal from the Dublin stalwart.
While Clontarf escaped unscathed on that first occasion, St Vincent's quickly found their feet and pressed ahead.
Clontarf, without their tailsman Jack McCaffery who was out due to injury, started the second half eight points adrift and things didn't improve for them from there.
St Vincent's finished 2-16 to 0-11, claiming the second spot in the next round after Ballyboden.
The earlier kick-off in Parnell Park between Ballymun Kickhams and Thomas Davis was an equally one-sided affair, with Ballymun recording an impressive 3-15 to 0-8 victory.
Speaking after the match Thomas Davis manager Paul Kelly said the better team won, adding his stint with the Tallaght club may be at its end.
Thomas Davis' are now out of the Championship, while Ballymun sit top of the group one table and will continue on to the next round.
