OSAS does not at all mean that there is no supernatural working of God.
It is the exact opposite, the acronym means the once a person is saved there are always saved because it is a supernatural/spiritual event.
Not a fan of this website due to its Calvinist leanings but even they agree.
Once a person is saved are they always saved? Yes, when people come to know Christ as their Savior, they are brought into a relationship with God that guarantees their salvation as eternally secure. To be clear, salvation is more than saying a prayer or “making a decision” for Christ; salvation is a sovereign act of God whereby an unregenerate sinner is washed, renewed, and born again by the Holy Spirit (
John 3:3;
Titus 3:5). When salvation occurs, God gives the forgiven sinner a new heart and puts a new spirit within him (
Ezekiel 36:26). The Spirit will cause the saved person to walk in obedience to God’s Word (
Ezekiel 36:26–27;
James 2:26). Numerous passages of Scripture declare the fact that, as an act of God, salvation is secure:
https://www.gotquestions.org/once-saved-always-saved.html