South Africa have won the toss and elected to bat in the fifth and final one-day international against Australia at the WACA here on Friday.South Africa, who have already taken the series 3-1, need a win in today's game to dislodge Australia from the top of the ICC ODI rankings.Meanwhile, from Australia's point of view they have everything to play for in this dead rubber. A win will not only ensure they hold on to their top spot in the rankings, but also give them invaluable confidence before they host New Zealand for the five-game Chappell-Hadlee Trophy next month.The team news is that South Africa have decided to rest Dale Steyn and Makhaya Ntini and will field two debutants - Wayne Parnell and Lonwabo Tsotsobe.