This win, in the second one-day international on Tuesday, sealed New Zealand's first series win on South African soil.
New Zealand, asked to bat first by South African captain Faf du Plessis, reached 279 for eight in their 50 overs after Williamson's brilliant 136-ball innings. South Africa looked on course for victory as they reached 165 for one after 30 overs but a spectacular collapse fuelled by five run-outs caused them to be dismissed for 252, handing the Black Caps an unassailable 2-0 lead in the three-match series.
Williamson was named man of the match and Kyle Mills was the pick of the New Zealand bowlers with figures of two for 28. New Zealand were struggling at 32 for two in the 13th over after BJ Watling (12) became Morne Morkel's 100th ODI victim. The wicket brought Grant Elliott to the crease and his 128-ball stand of 127 with Williamson gave the visitors great impetus.
Despite a middle-order collapse following Elliott's dismissal for 48, the 22 year-old Williamson controlled his innings superbly and, aided by Nathan McCullum (19) and Mills (15 not out), helped his side to a competitive total. The South African reply began steadily with openers Quinton de Kock (25) and Graeme Smith (66) taking 17 from the eighth over from McCullum.
Taking the attack
Mills bowled De Kock in the next over to end an opening partnership of 38 but Smith was joined by fellow left-hander Colin Ingram (79) and the pair built a good platform for the hosts. The fifty partnership came up in the 18th over from just 57 balls and Smith found the fence five overs later with an audacious sweep off Elliott to bring up a 60-ball half-century.
Ingram also reached his half-century and the hundred partnership with a boundary as he slashed a wide Mitchell McClenaghan to third man and the Proteas were cruising at 139 for one. The duo continued to take the attack to the bowlers and were beginning to look impregnable until two run-outs in two overs changed the course of the game.
Smith was beaten by a fine James Franklin throw from the boundary to end the 129-run partnership before a poor call from Du Plessis (2) gave away his wicket eight balls later. McCullum claimed the crucial scalp of Ingram and the hosts were four wickets down requiring 100 runs from 93 balls.
David Miller (14) offered brief resistance before being run out in unfortunate circumstances at the non-striker's end after a crisp straight-drive from Farhaan Behardien (31) and South Africa were 211 for five when he departed. Rory Kleinveldt (0) and Berhardien (31) added their names to the list of batsmen to be run out and the hosts were bowled out for 252, five deliveries short of their allotted 50 overs. – Reuters