Two tries in four brilliant minutes proved the difference in the Pool B opener on Saturday but the holders struggled to find much rhythm and had to ride out a brief Springbok scare in the second half.

"We won, didn't we? So you've got to be happy with that. Were we perfect, no but you're never going to be at this stage of the tournament. You're not in the swing of the tournament and right from the get go you've got the biggest game possibly of the group," Hansen told a news conference.

"There is plenty of stuff we can work on. The boys showed a lot of fortitude, we didn't get too many opportunities and we took them when they came and we scrambled really well when they had opportunities themselves. Both those areas are really important to us."

Hansen highlighted flyhalf Richie Mo'unga's potential "match winner" of a cover tackle on the electric Cheslin Kolbe, just after South Africa had cut the deficit to one score in the second half.

With two staunch defences going head to head in a game that produced only 12 combined line break, Hansen said it was a case of having to take what you are given and for New Zealand that was two stunning breakaway tries.

"It was really hard early in the game for us, our set-piece wasn't as nice as you'd expect it to be and therefore you can't have a platform to strike off. The boys adjusted okay and as the game got on, they started to get a bit more fluid with it," he said.

"It's an area that we're just continually working on, we're making progress but you can't strike if you don't get TQB, which is top quality ball at the set piece."

Australian Associated Press