Two-time defending champion New Zealand began its 2019 Rugby World Cup campaign with a statement win over South Africa on Saturday night, but head coach Steve Hansen thinks it will count for little when the business end of the tournament begins in the knockout round.

The All Blacks came through a clash of the titans at International Stadium Yokohama with a 23-13 victory over title rival South Africa, after two quickfire tries midway through the first half turned the match in their favor and gave the Springboks too much to do in the second half.

The result left South Africa needing to make Rugby World Cup history if it wants to lift the Webb Ellis Cup for a third time, as no team has ever lost a first-round match and still gone on to the claim the title.

But Hansen dismissed that statistic as little more than a historical curiosity, arguing that all teams with serious designs on the title will have to win or go home when the knockout phase begins anyway.

"I talked about this the other day," said Hansen. "For us to win the tournament, we've got to win every game. For them to win the tournament, they've got to win every game, so no one is any worse off than the other. History is a great thing, but history is there to be broken. Their mindset from now on is every game is a final, and I guess it's the same for us."

A crowd of 63,649 arrived in Yokohama to watch one of the most eagerly awaited pool-stage matches of Asia's first-ever Rugby World Cup, and South Africa looked to have the upper hand until George Bridge and Scott Barrett blitzed the Boks with two tries in the space of three minutes midway through the first half.

A try from Pieter-Steph du Toit and a drop goal from Handre Pollard reduced the deficit to four points at one stage in the second half, but the All Blacks kept their poise to see out the win and maintain their record of never having lost a Rugby World Cup first-round match.

"The game is all about moments," said New Zealand scrumhalf Aaron Smith. "We just tried our guts out to calm down, get back to the plan, and once we got back to our structure, we looked better. South Africa are an amazing team as we saw, and if you give them a sniff — jeez, we were hanging in there at times.

"It was an awesome game to be a part of, and such a big buildup. It's been a long two weeks. It's been a long year to get to this point, and I'm really glad that we put a performance out there that we're proud of."

South Africa had chances to add to Du Toit's try in the second half, with lightning-fast winger Cheslin Kolbe streaking through the All Blacks defense until a vital tackle by Richie Mo'unga stopped him just short of the line.

Hansen described Mo'unga's tackle as "a match-winner, or close to it," and Kolbe was left to rue what could have been.

"If we could have got that try then I think the game would probably have been different," said the 25-year-old. "I think I could have gone a bit quicker to his outside and just backed myself, but I just have to make sure that whenever there's another opportunity like that again, I capitalize on it."

Mo'unga's partnership with Beauden Barrett was the focus of much attention in New Zealand before the game, with former flyhalf Barrett being pushed back to fullback to accommodate the lavishly skilled Mo'unga in the No. 10 position.

Both players were pleased with the way their playmaking qualities dovetailed in attack, and Barrett believes their relationship can blossom as the World Cup progresses.

"It's only going to get better," said Barrett, who was named man of the match. "I love playing with Rich. He's a super talent and hopefully for this team we can figure out how we get the best out of each other and do what's best for this team.

"It's great that we have a 10-day turnaround now. We'll head down to Oita and see a different part of the countryside, which will be really exciting. I don't think any of us have been down there, so it will be pretty cool."

New Zealand continues its campaign against Canada in Oita on Oct. 2, while South Africa is back in action against Namibia in Toyota, Aichi Prefecture, on Sept. 28.

For South Africa head coach Rassie Erasmus and his men, there is no more room for slip-ups.

"I think we can fight back," said Erasmus. "I think even in the game we fought back. At halftime to be 17-3 down, I've seen South African teams go to 50 points when they're that amount of points down against New Zealand. So, to be down 17-3 and then get back to 17-13 or whatever the case may be, and then get close to scoring a try, I think there were stages when we really fought back well."