Nielsen was the unlikely hero with his 105 pivotal in helping the Redbacks reach 9-357 at the close of play on the first day of JLT Sheffield Shield action for this calendar year on Thursday.
The 22-year-old gloveman played with composure throughout the day after coming to the wicket with South Australia 5-126, having earlier been 3-34.
Nielsen is just the ninth player to score a century in a debut innings for South Australia in the Shield.
No.5 Jake Lehmann scored a diligent 83, sharing in an 86-run stand with him for the sixth wicket.
Allrounder Joe Mennie then cracked a lusty 75 off just 96 balls to take the match away from Victoria, after the visitors had sent the home side into bat.
Mennie and Nielsen put on 143 for the seventh wicket off just 30 overs.
A succession of late wickets fell past the scheduled closing time with the Victoria's pace trio doing all the damage.
Chris Tremain led the way with 4-80, able supported by Scott Boland (3-71) and Peter Siddle (2-75).
Shield holders Victoria sit at the bottom of the standings without a win this season, while South Australia have won just one of their five outings.