If you are unranked and lose a match, you'll actually be placed at the bottom of the ranked players, just like when you join the ladder. For example, on launch day, I played Ryguy for the first match ever, and won it . . . and it put me at the bottom of the ranked players, which was #1. And then it did the same thing to him, which made him #2.
Ahhh, launch day.
Unranked players are in the order they joined the ladder. Bit of trivia, btw, Jeds was the first pilot to join the ladder -- if you look at the URL on his profile, his player ID is 1.