The problem with this entire defense is two-fold.
1) According to his version, OP put his own life in danger by being the aggressor in the confrontation. The "intruder" cannot be blamed for OP chasing after him and standing in front of the door.
2) OP denies he shot the "intruder" in self-defense now. He abandoned his claim that he shot in self-defense.
I see your point (edit: I mean to say that I agree with you. Sorry for the edit. English is not even my second language.) but I think OP said a lot of things on the stand and I'm not sure if what he said means he legally changed his defense or if it just means he f-ed up.
In the end it comes down to Judge Masipa and her two assessors. They will have to decide if it's possible that Oscar could have mistakenly thought he was entitled to shoot the intruder because he thought he was under attack.
Keep in mind that they would then also have to believe a lot of other things are possible. I.e. he screams like a woman. He screams in two voices. The light was not on. Baba lied. Mangena is mistaken. Saayman. Dr. Michelle Burger. Johnson. Dr. Stipp and Mrs. Stipp. They were all mistaken/wrong/lying or had a hidden agenda to put Oscar away.