New Zealand were exhilarating as they raced into a 17-0 lead in the first quarter, the Springboks unable to handle their power and high tempo game.
South Africa clawed their way back into the contest and trailed by eight points just past the hour-mark, until the All Blacks turned the screw again for a deserved victory that lays down a marker ahead of the World Cup in France.
The win followed an equally impressive 41-12 success in Argentina last weekend that left Foster with one hand on the Rugby Championship trophy in this truncated three-game competition.
"It’s a great start for us this year, but it is just that (a start). We got a bit fidgety in the third quarter and went into our shell and they got back into it," he told Sky Sports.
"We have a lot of respect for South Africa and to put that scoreline on them … they turned it into a real arm-wrestle but I love the way we started, hung in there and then finished strong in the last quarter.
"They (South Africa) have got a massively experience bench and they that showed in the second half. They put them on early, put us under a bit of pressure, but I felt with the changes we made, the whole team lifted."
Several New Zealand players impressed, but loose-forward Shannon Frizell was immense and scored a barn-storming try in the first half when he ran over Bok fullback Willie le Roux.
"Shannon has answered a lot of critics and he should be really proud of that game tonight, he was outstanding," Foster said.
The All Blacks travel to Australia for their final Rugby Championship fixture on July 29, before they host the Wallabies in a second Bledisloe Cup contest a week later.
"We have a bit of a breather, and then the two Bleds and the Rugby Championship (still to win)," Foster said. "I love the attitude in the last three or four minutes when we went for that bonus-point try.
"It hurt us with a try against us too, but it shows how much it means to us. We said at the start we really want to nail this Championship and we stick to that."