Late goals to Stephen Milne and Arryn Siposs sealed the 16.9 (105) to 14.8 (92) victory in a match that saw the lead change 10 times - six times in the final quarter.
Milne finished with three goals while skipper Nick Riewoldt took three quarters to make his mark on the match before slotting two goals in the crucial final term.
But it was Saad who was the star for the Saints, with his soccer skills developed as a junior in his home country of Egypt playing a big part in the win.
Three of his four goals came from well-timed kicks on balls half-volleyed off the deck.
It was the first time the 22-year-old had scored four goals in a match since being called up into the Saints roster for his first AFL stint this year.
Rohan Bewick, Tom Rockcliff and Daniel Merrett - benched by coach Michael Voss for the opening exchanges - had two goals each for the Lions.
Simon Black, Dayne Zorko, Andrew Raines, James Polkinghorne, Todd Banfield, Aaron Cornelius, Patrick Karnezis and Jonathan Brown were the other goalscorers for the home side.
The loss was a hammer blow to the resurgent Lions' finals hopes, with the Brisbane club finding late form with three wins in their previous five matches leading into the clash.
After trailing 4.0 (24) to 3.3 (21) at the first break, the Lions peeled off three quick majors through Merrett, Polkinghorne and Raines to build an 11-point lead.
In the third quarter, as the Saints' radar faltered with five behinds and two complete misses, Brisbane again threatened to run away with a big advantage until Saad's fourth goal and Milne's first of the match gave the Saints a one-point advantage.
Saints midfielder Clint Jones had a strong game after a sickening collision with the boundary fence early in the first quarter.
He battled on after his head thudded into the steel fence following a push in the back from Lions midfielder Daniel Rich and finished with 15 contested possessions and 28 disposals.