He excelled statistically.
Williamson reached his 17th test century, equalling Martin Crowe's New Zealand record.
He became the sixth Kiwi to get 5000 test runs when he pulled Vern Philander for six over square leg.
Williamson is the fastest in 110 innings, seven inside Crowe's old mark. At 26 years and 231 days he is also the third youngest test player to complete the feat behind Sachin Tendulkar and Alastair Cook.
His 190-run record second-wicket stand with Jeet Raval (88) saw New Zealand wrest back control at 321 for four in reply to South Africa's 314.
He excelled with his leadership.
An example was when he appeared to get offered the light by the umpires at 6.47pm; Williamson decided to continue, thus maximising the chance to score runs and advance the match.
Yet none of those factors would have infiltrated the captain's mindset as he strode through the pickets at stumps. The match result is the sole barometer of success for cricket's patron saint of modesty.
Williamson made his lowest test aggregate (3) at Wellington, but shrugged off that cloak of disappointment the moment he leant into a cover drive off Morne Morkel to go from two to six. From there he was a picture of batting application. His influence was further bolstered by a rare test six - the 10th of his career - on-driving Keshav Maharaj towards the sightscreen and holding his shape. Further sixes were pulled from Vern Philander and Morkel.
The batting tended to be of low risk and maximum impact, which tamed South Africa in the field. Despite accurate lines, bouncing the ball on the used block strips to enhance its reversing qualities, and intense pow-wows between captain Faf du Plessis and his bowlers, the visitors' attack could not penetrate the captain's mental or physical defensive shields.
Williamson benefited from what was effectively a padded-up vacation with Raval and Tom Latham posting an opening stand of 83, beating the previous first-wicket best of 18 by either side in the series.
"He [Williamson] is never satisfied with a century," Raval said. "He wants to get big runs to help the team into a good position. I was lucky enough to be at the other end.
"He's so calm, and knows his game. He senses each situation well by soaking up the pressure and then knowing how to reapply it when they're a bit tired."
"They left well," Morkel said. "They played a patient game and waited for us to attack by coming a bit straighter. Then they scored.
"Kane was exceptional. It was a fantastic innings. He's a hard man to bowl to."
