The South African cricketers' success in winning seven out of nine 50 over matches against Australia this year has consigned Ricky Ponting's side to its lowest ranking in the ICC one day championship.
The four-time world champions are now third, behind the Proteas and India, with New Zealand fourth, one point ahead of Pakistan.
But Australia can regain second with a win on the final match against South Africa in Johannesburg on Friday night.
