Since PCSX2 simulates a PlayStation 2, it treats save files exactly like a real PS2 Memory Card.
This guide applies to PCSX2 versions 1.6, 1.7 (nightly), and Qt builds. God of War games are notoriously picky about save state corruption, so proper memory card handling is critical.
If you have downloaded a 100% completion save or a specific checkpoint (like the final battle with Ares), you cannot simply drag it into a folder; you must "inject" it into the virtual card.
: The emulator typically uses 8MB files to ensure maximum compatibility.