"With South Africa, we picked up that Smith was a bit too comfortable behind the rucks, so we got in their faces and I tried to get in his face. I knew they just expected him to be at every ruck, to deliver quick ball, so I had to hit him and keep him on the ground a second longer."
It worked a treat as the Springboks turned around a rough run of form with a famous victory, and now de Klerk is eyeing up the World Cup, where the Springboks now have full belief that they can topple the defending champions once again when they meet in the opening pool game.
"That first game is going to be amazing," said De Klerk.
"We can turn everything on its head and surprise a lot of people. One of [coach] Rassie [Erasmus]'s main points was that if we can beat New Zealand away, our chances of winning the World Cup will go up so much more.
"We've done that, so we know we can beat them in that pool game on neutral ground."
Erasmus agrees that the Springboks now have a legitimate chance of earning a top result at the World Cup.
"We've shown on the day when everything's aligned and the guys are all in the same frame of mind, we can beat the All Blacks away and win a series against England," said Erasmus.
"It's wide open," he said of the World Cup. "I've been involved in World Cups since 1995, but really this one I couldn't put money on who's going to be in the semifinals."