South Africa will reclaim the number one spot in the ICC Test rankings only if it manages a 3-0 whitewash against Australia.
On the other hand, although the series is already lost, a draw would be enough for Australia to extend its stay at the top of the ICC chart.
Australia has held the top spot since August 2001 when the current ranking was introduced and has been number one for all but eight months out of the last 13 years when South Africa led the championship table for three months in late 1999 and for five months in 2001.
If South Africa win in Sydney, it will put both the teams level on 123 ratings points but Smith's side will be placed higher by a fraction of a point.
However, all the talk of South Africa regaining the number-one spot for the first time in almost seven-and-a-half years will go out of the window if Australia wins or even draws the Sydney Test.
If Australia wins, it will retain the number one spot on 126 points while South Africa will be second on 121 ratings points. A draw, meanwhile, will keep Australia ahead of South Africa on 124 ratings points but the difference will be reduced to just two points as compared to the pre-series gap of 13 points.
