Retallick, who was named World Rugby player of the year in 2014, put in a ferocious 80 minutes despite injuring his ankle in the warm-up.
Matters were made even harder for New Zealand when fellow second-row Sam Whitelock was sin-binned in the second half, but they snatched a 27-20 victory from the jaws of defeat thanks to a try from skipper Richie McCaw in the 73rd minute.
And Hansen said: "(Retallick) assured us he was ok but I think it's a testament to his courage and his mental fortitude and toughness that he actually got through the game.
"He got another belt on it in the far corner and re-taped it, so he should be pretty proud of himself and we're very proud of him.
"At half-time we didn't deserve to be in the game, we played poorly and were dominated, but in the second half we showed a lot of character and fortitude."
And Hansen also singled out debutant fly-half Lima Sopoaga, who conjured up a brilliant offload for Ben Smith to score New Zealand's first try.
"He showed a lot of character for a young man," said Hansen. "He missed a couple of kicks there but came back and kicked the important ones."
That result means The Rugby Championship will come down to the Bledisloe Cup clash between Australia and the All Blacks in two weeks' time, after Argentina fell to the Wallabies in Mendoza.
Australia held a two-point lead heading into half-time before Dean Mumm, Tevita Kuridrani and Adam Ashley-Cooper crossed in an eventual 34-9 victory.
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