Defence was 50 percent of the game and probably 90 percent when the psychological value of it was taken into account such as the All Blacks had achieved by missing only one of 75 tackles, Hansen said.
"We kept our discipline. When they carried we got up and made our tackles, and they were punishing tackles, and forced some errors and when you're doing that teams start second guessing a little bit and psychologically you get an edge. It's been very, very good all tournament," he said.
England, in next weekend's semifinal would be a massive challenge but Hansen said he didn't think it was time to be talking about that. The All Blacks had a formula around Test matches and once a week was completed they needed to take some time to step off the merry-go-round and relax.
"We'll do that. We'll enjoy our moment, it was a special Test match that the All Blacks can be proud of and New Zealanders can be proud of, particularly the players can be proud of. We won't think about England until tomorrow," he said.
Speaking to his selection of less experienced players compared to Ireland's decision to go with experience, Hansen said the big moments his less experienced players had been involved in allowed them to be selected with confidence and to play well in the Test matches they had been chosen for.
"Their enthusiasm, excitement and their ability to play the game in the form they're in is really important but so is the leadership and experience from the guys who have been through the tough moments and been through knockout football," he said.
Eleven of the All Blacks side had experience of winning in knockout football.
They had also been reminded, and reminded and reminded that they had lost to Ireland.
"All Black teams don't need to be reminded that they've lost two games to Ireland out of 38, they know that and they don't forget it. We remember our losses way more than we remember the wins. So it's banked, it's not something you go and talk about, everyone knows it," he said.
New Zealand respected Ireland, they were hard to play and they prepared for that because they knew if they didn't they would be going home.
Captain Kieran Read said the side's first half had set up the game. They had managed to put plenty of pressure on Ireland, a strong, forward oriented team who were capable of attack as well.
"We nullified what they could bring early through our discipline and were able to score some tries which gave us the opportunity to get in front," he said.
"It was a very tough Test match and I think the scoreboard can flatter us and I think we were very good tonight on the way we took our opportunities," he said.
Backs coach Ian Foster said the team had been up for the game all week but they had to perform up front against Ireland which they did and that enabled the backs to play with more freedom.
The quality of ball from scrum, lineouts and rucks was outstanding and it had delivered front foot ball for the backs, he said.
Hansen started the press conference by marking the significant careers Ireland captain Rory Best and coach Joe Schmidt had enjoyed with their side and which were ending after the World Cup.
"They had magnificent careers in their respective roles for Ireland. They've made a difference in their time and it doesn't matter what team you play for, if you can make a difference while you're there then you've done your job," he said.
Hansen also paid tribute to All Blacks captain Read who had come back from a significant back injury, taking some flak from critics, but had got better and better and he had led the side well and had gone to a higher level in that role at the World Cup.
He also thanked his fellow coaches, backs coach Foster, defence coach Scott MacLeod and forwards coach Mike Cron.