"We knew it was going to be tough," said McCaw, who became the first New Zealand captain to keep a Springbok side scoreless on South African territory.
"In this Tri Nations, there is nothing between the teams. We had a good performance two weeks ago and we had to go out and do it again.
"We will now witness the next couple of weeks. But this was a must-win game for us.
"We can sit back for a couple of weeks now and it could an interesting one (against Australia) in a few weeks time."
Smith, who beat Springbok outside-half Butch James to McCaw's deft grubber kick to cross for the first of three unanswered tries against the World Champions, re-iterated his skipper's sense of pride in a crucial victory.
"We are more than happy with a win like that," said the Wellington Hurricane.
"Coming over here, I know they would have been targeting if they won their home games the Tri Nations could have been theirs.
"But we have managed to take one off them. We are still alive and have a game in Brisbane to go.
"There is no more we can do from here."
Smith also praised his captain's individual contribution after McCaw put in another outstanding all-round display in an All Black jersey.
"He can do it all," said Smith.
"It is great to have him back in the side.
"We don't practice things like that too much, but this is a special side and it is why I love playing in this jersey along guys like that.
"You make the most of your chances and that is what it takes to play in a test match like this."