Sarries ran in six tries on the night, with the boot of fly-half Andy Goode adding 27 points via five penalties and six conversions.
Ben Johnston and Cardiff-bound Tom Shanklin opened the scoring in the opening 20 minutes for the home side, with Leeds' Canadian wing Winston Stanley grabbing the first of his two tries early on to keep the visitors in with a chance.
Irish wing Darragh O'Mahony scored Sarries' third on 33 minutes, Goode having kicked three penalties previously.
Wing Chris Hall touched down for Leeds on the stroke of half-time, but in the second half Saracens were to accelerate away.
Kris Chesney was quick off the mark with a 41st minute try for Saracens, Stanley touching down his second for Leeds before late scores for centres Tim Horan and Kevin Sorrell all but booked the Londoners' place in the Wildcard Final.
For Saracens:Tries: Johnston, Shanklin, O'Mahony, Chesney, Horan, SorrellCons: Goode 6Pens: Goode 5
For Leeds Tykes:Tries: Stanley 2, HallCons: Ross 3