Rassie Erasmus felt South Africa's Rugby World Cup defeat to New Zealand owed much to the All Blacks' superior discipline.

The Springboks applied plenty of pressure in the first quarter of Saturday's blockbuster Pool B opener but saw their 3-0 lead quickly turn into a 17-3 deficit, the defending world champions hitting top gear in a stunning six-minute blitz.

A Pieter-Steph du Toit try and Handre Pollard's second penalty gave South Africa hope after the interval, only for Richie Mo'unga and Beauden Barrett to land three-pointers as New Zealand triumphed 23-13.

In a post-match news conference, Erasmus said: "I think they won it. I don't think we lost it. Two tries to one, they definitely deserved to win the game.

"If you concede, I think, 11 penalties to two, you're going to struggle to beat New Zealand. I think discipline was our biggest downfall. I don't think we can moan about anything.

"As I said, I think the penalty count was 11-2, so we did 11 things wrong. We have to go and fix it. They only did two things wrong, which is unbelievably well disciplined by them. That battle, we lost.

"I give all credit to New Zealand. When we had territorial and scoreboard pressure and they had that one opportunity to pounce, they pounced."

No team has ever won the World Cup after losing in the pool stage, but Erasmus believes his side can buck that trend.

"I think we can fight back. I think even in the game we fought back," he stated. "To be down 17-3 and get back to 17-13 and being in their 22 ... there were stages when we really fought back well."

With a smile, he added: "If you're grouped with New Zealand in your pool, you've got a good chance of not going undefeated through your pool.

"And then you have to fight back and try and get to the final, for the first time in history not being unbeaten. We have to go [down] that route now."

Erasmus said Trevor Nyakane (calf) was the only Springboks player to pick up an injury, attributing late concerns over Cheslin Kolbe and Du Toit to cramp.