Ma'a Nonu and Conrad Smith have rarely been upstaged in their long New Zealand careers but they expect another testing afternoon from South African centres Damian de Allende and Jesse Kriel in their World Cup semi-final.

Nonu and Smith have the caps, experience and a partnership that shows no sign of ending soon. De Allende and Kriel have youthful exuberance and a spark that has breathed a new lease of life into the Springboks midfield.

The All Blacks pair first came up against Saturday's opponents in their Rugby Championship clash in Johannesburg in July. The All Blacks prevailed 27-20 but it was the Springboks duo who made more of an impression.

Kriel scored a fine try after bursting through the tackles of Nonu and Smith while De Allende consistently made gains with his strong running.

Smith and Nonu, both 33, have 193 caps between them and have lined up alongside each other in 60 tests, a world record by a starting centre combination.

De Allende, 23 and Kriel, 21, have a combined 20 caps but Nonu has seen enough to warn of their threat on Saturday.

"They are a great partnership and I've seen them grow this year," Nonu told reporters on Friday.

"It's going to be a massive match up for myself and Conrad. We've prepared well, we'll see how it goes in the game."

The statistics heavily favour Nonu and New Zealand.

The 33-year-old has been on the winning side in his last 10 test appearances against South Africa and New Zealand are undefeated in the last 25 tests he has played.

But Smith is also expecting another tough afternoon.

"They're two guys we're very aware of and what they do for their team. They're a couple of major strike weapons so they'll take a bit of containing," he said.