Graeme Smith made 115 and Jacques Kallis and unbeaten 107 in a 200-run partnership that wrested control of the first cricket test from New Zealand on Friday.
South Africa was 268-3 at stumps on the third day with a lead of 233 runs.
Smith's 23rd test century and Kallis's 42nd led South Africa from crisis to comfort, allowing the Proteas to break a deadlock that had existed for most of the first two days.
South Africa trailed by 35 runs after the first innings and was 47-2, leading by only 12 runs, when veterans Smith and Kallis came together on Friday morning. They stayed together for the next two and a half sessions and by stumps had ensured the Proteas were the only team still with a winning chance.