Williamson had four failures in the test series but he bounced back with a best bowling performance of 4-22 in the first ODI to make a valuable contribution.
He may end up one of our best batsmen behind Bert Sutcliffe and Crowe - who knows what the future holds - but Williamson will certainly end up our most modest champion.
He was uncomfortable talking about his superb knock yesterday, preferring to lavish praise on Grant Elliott with whom he shared a stand of 127 to essentially set up the victory.
"It was obviously nice to contribute like that in such an important game but I think the second half of the match was pretty key obviously, with all the run outs on a very good wicket," Williamson said.
"It has been tough all right playing the number one team in the world so the boys have really stepped up in the last two games and it is very rewarding to come home with a series win.
"I cramped up a little bit at the end but luckily the guys at the other end complemented my innings well and we put together a pretty good total."
South African captain Faf du Plessis was full of praise for Williamson and admired the way he kept going despite suffering from cramp in the hot conditions.
"He made use of the wicket and took his time up front and played brilliantly," de Villiers said.
"Credit to him as you could see he was cramping but he did not throw his wicket away. He made sure he stayed there until the end for the team, so it was a great knock."
Black Caps captain Brendon McCullum was equally effusive in his praise for Williamson's innings and the importance of the victory in New Zealand cricket annals.
"Kane Williamson stepped up beautifully and his innings was as good an innings as I have ever seen from a New Zealander in one-day cricket," McCullum said. "I think a few guys backed it up around him as well and I thought the way we were in the field was outstanding.
"I am not going to underplay (the win). It has not been an easy tour and it is a phenomenal effort to come over here as the number ninth ranked team in the world up against the number one team in their own conditions. To be 2-0 up in the series is incredibly satisfying and will probably go down as one of our biggest ever wins in the limited overs game.
"We probably had no right to win (game one) in Paarl but our character and fighting spirit and qualities that we want to be known for came through. A couple of the older fellows in James Franklin and Kyle Mills stepped up in that game and got us through and that probably allowed us to play with a little more freedom today.
"I am very, very proud of the boys who have shown so much character over the last two games. We know we still have a game to go but we will certainly enjoy the moment of this win." McCullum agreed that the arrival of some faces into the ODI series after the ignominy of the 2-0 test series loss has played a key role in lifting the spirits of his team but they were due some success.
"Some fresh enthusiasm from the guys coming in, both old and new heads, has helped but everyone throughout the tour has worked really hard and tried everything they possibly could. We were outplayed in the test matches completely, and were beaten 2-1 in the T20s, but we are now getting some fruit for our labour at the end of this tour."
The final game in the ODI series starts at 1am on Saturday (NZ time).