The two-time defending champions will head into the final day at Junction Oval needing just three wickets to wrap up their season opener.
Victoria limped to 7-175 in their second innings on Friday and still need another 89 runs to force South Australia to bat again.Â
Resuming at 6-352, Manenti (92 overnight) and McFadyen (46) picked up where they left off.
SA captain Manenti showed no sign of nerves to bring up his maiden first-class century, before being caught for 128 off 154 balls.
The 29-year-old allrounder, who has represented Italy's national team, had made 12 first class half centuries before breaking his hoodoo.
McFadyen, who made 134 off 174 on first-class debut, was at risk of being stranded short of his ton after losing tailenders Nathan McAndrew (four) and Henry Thornton (five) in quick succession.
But the allrounder - a former Brisbane Lions academy member - smashed back-to-back sixes to pass the milestone.
Paceman Brendan Doggett (19 not out) was an ally up the other end as the pair put on a 68-run last-wicket stand to push SA's total to 508.
Trialling by 264 runs, Victorian opener Marcus Harris (27) began steadily before being trapped in front by McAndrew (2-35).
Peter Handscomb (duck), Ollie Peake (three), Matt Short (six) and Liam Blackford (20) all fell around opener Campbell Kellaway, who battled hard for a half century.
In search of a result, the umpires extended play for half an hour when Sam Elliott (two) became the seventh wicket to fall, on the stroke of 6pm (AEDT).
But Fergus O'Neill (42 not out) and fellow quick Harry Hoekstra (seven not out and 6-103) hung in to avoid an embarrassing defeat inside three days.
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