It was feared that the game would be a complete washout as the wet weather came down hard at the Swalec Stadium overnight and this morning.
However, with the rain subsiding for now, the umpires have given the go-ahead for a reduced-overs match, with the Proteas fielding first after winning the toss.
South Africa make no fewer than six changes to the side that toppled England from the number one Test rankings berth with a 2-0 series victory.
England: Cook(c), Bell, Trott, Bopara, Morgan, Kieswetter(wk), Bresnan, Woakes, Swann, Anderson, Finn
South Africa: Smith, Amla, Elgar, De Villiers (c and wk), Duminy, Du Plessis, McLaren, Petersen, Parnell, Morkel, Tsotsobe