Cape Town - Defeat against the Springboks at Loftus on Saturday will see New Zealand's lead at the top of rugby's world rankings significantly reduced.
Regardless of the result in Pretoria, New Zealand will stay top, but if they lose then their lead over second-ranked Ireland will be cut to almost nothing.
The All Blacks are currently top of the rankings with 92.52 points, while Ireland are second with 90.12 after a series win against the Wallabies in June.
If the All Blacks lose by 16 points or more, they will slip down to 90.18 points to be just marginally ahead of Ireland.
A one-point win for the Boks, meanwhile, will see New Zealand drop to 90.96 points.
It means that defeat on any kind for the All Blacks on Saturday will put Ireland in striking distance of claiming top spot ahead of the end-of-year internationals in the northern hemisphere in November.
The All Blacks have some tough fixtures on that tour, taking on England and Ireland in back-to-back weeks.
The match against Ireland will be played in Dublin on November 17.