OK, so you wish to go JNB to EZE
MileageMonkey tell me oneworld flies JNB to MAD/LHR/BCN and MAD/LHR/BCN to EZE.
This is your best option. With your proffered routing you cannot go via SWP (e.g. JNB-SYD-EZE) as you would be crossing the Pacific twice.