By Greg Stutchbury

AUCKLAND (Reuters) - Two tries from captain Kieran Read helped New Zealand grab the lead in the Rugby Championship on Saturday after a 29-15 victory over South Africa, who had Bismarck du Plessis sent off for two contentious yellow cards.

The bonus point victory came courtesy of tries from Read, Brodie Retallick and Sam Cane but at the cost of a collarbone injury to flyhalf Daniel Carter in a crunching tackle from hooker Du Plessis.

New Zealand coach Steve Hansen told reporters it appeared Carter had injured the AC joint in his right shoulder and that he could be out for between four and six weeks.

Du Plessis was sin-binned for the tackle then received a second yellow in the first minute of the second half for leading with his elbow into the throat of Liam Messam.

Neither Hansen nor his counterpart Heyneke Meyer were prepared to discuss the yellow cards in detail, with Read and Ma'a Nonu also sin-binned in the final 10 minutes, though Hansen said anyone leading with their elbow was at risk of a red card.

"In an intense battle like that, you're going to get moments and a referee has to make decisions in those moments," Hansen said.

"Perhaps Bismarck may have been unlucky on Dan's yellow card but he probably got the other ones right.

"I don't think it is legal to go putting your elbow in some one's throat," Hansen added tersely when asked about the two cards to du Plessis.

"The second card may well have been a red one rather than a yellow.

"But we have got no complaints. That's rugby and you just have to get on with it."

INTENSE MATCH

With both sides unbeaten in the tournament, the match had been billed as the most important in New Zealand since the 2011 World Cup final and neither side disappointed in an intense encounter.

The collision zone was brutal with several players reeling away from the contact grabbing their heads, shoulders and ribs as they were hammered by their opponents.

The pivotal moment of the game, however, occurred in the first half when Carter was crunched by Du Plessis in a tackle ruled by referee Romain Poite to be high, although television replays suggested the hooker had been hard done by.

The tackle sparked an all-in brawl with several players wrestling, pushing and shoving, while the 47,362-sellout crowd bayed for the Springbok's blood as he trudged to the sideline.

The first yellow had left the combative Sharks player walking a thin line for the remainder of the game and although he had scored a first-half try when he returned, his reaction to a Messam tackle effectively ended the game as a contest.

Du Plessis braced himself for the tackle in the first minute of the second half, but led with his elbow that struck Messam in the throat and left the blindside flanker reeling away.

Poite referred the decision to television official George Ayoub who recommended a yellow card and the Frenchman had no choice but to show Du Plessis a second yellow then the red.

Until that point the match had looked likely to be decided by the smallest of margins but the extra man for much of the second half played into the hands of the world champions.

South Africa captain Jean de Villiers, however, said despite the dismissal of du Plessis, his side had not played well enough to win the game.

"The All Blacks are a tough team to play when you have 15 on the field so when you have 14 it's a tough ask," de Villiers said. "But that was not a performance that was good enough to compete with them.

"We have seen tonight how far we are behind the All Blacks and credit must be given to them for the way they played.

"They are a fantastic team."

(Editing by Ed Osmond)