Whichever team wins this match will join already-qualified India as one of the two Group B sides going through to the semi-finals.
The minimum number of overs required to declare a result is 20 per side - a format that would appear to favour the West Indies given they are the reigning World Twenty20 champions.
If that mark cannot be reached, South Africa will go through to the last four because of their superior net run-rate (+0.41 to West Indies' -0.08).
West Indies captain Dwayne Bravo won the toss and elected to field.
Tino Best replaced fellow fast bowler Kemar Roach, ruled out through illness, while under-performing batsman Ramnaresh Sarwan was dropped, with Devon Smith taking his place.
As expected, South Africa recalled premier fast bowler Dale Steyn for his first appearance of the tournament following a side strain, with spinner Aaron Phangiso dropped to make way for the paceman's return.
Teams:
South Africa:
Hashim Amla, Colin Ingram, Faf du Plessis, AB de Villiers (captain/wkt), JP Duminy, David Miller, Ryan McLaren, Robin Peterson, Chris Morris, Dale Steyn, Lonwabo Tsotsobe
West Indies:
Chris Gayle, Johnson Charles (wkt), Devon Smith, Marlon Samuels, Darren Bravo, Dwayne Bravo (captain), Kieron Pollard, Darren Sammy, Sunil Narine, Ravi Rampaul, Tino Best
Umpires: Steve Davis (AUS), Rod Tucker (AUS)
TV umpire: Bruce Oxenford (AUS)
Match referee: Andy Pycroft (ZIM)