The 57-year-old New Zealander, who last Sunday was named world coach of the year for the fourth time in five years, said the facts served as evidence for his statement.
The Irish - also coached by a Kiwi in Joe Schmidt - ended a 111-year wait after 28 previous attempts with a superb 40-29 victory over the All Blacks in the unlikely environs of Chicago, Illinois, a fortnight ago.
The performance drew admirative tweets from such diverse characters as authoress JK Rowling and US vice-president Joe Biden as defeat stopped the All Blacks' world record Test run of 18 successive wins in its tracks.
"Yes we are the underdog," said Hansen at a press conference on Thursday.
"Just go back to Chicago, it was 40-29 and they won easy.
"Strange or whatever, that is a fact and you can't argue with facts. They are what they are."
Hansen, who guided New Zealand to a successful defence of their World Cup title last year, said he didn't want to be in charge of the first All Blacks side since 2009 to lose consecutive Tests to the same opposition - their predecessors losing to then world champions South Africa.
"How would you feel? You would certainly not be laughing about it," he said.
"However, it is also true we don't have a God given right to win every match. If the team is good enough on the day to beat us so be it."
Hansen, who enjoyed a far less happy experience in charge of the Wales team from 2002-04, said he hoped his players had learned some hard lessons from the Chicago defeat.
"We know we didn't play very well and we know we have to vastly improve because they are a very good side," he said.
"If everyone performs their core roles such as lineouts, defence and kicking that should fix our performance and take it to another level.
"Certainly we must improve our discipline as we conceded 12 penalties in Chicago that allowed them to kick for position and put us on the back foot the whole time.
"You expect a couple of penalties but 12 that is really an offday."
Hansen said neither taking the opposition for granted nor his players lacking motivation would be a problem on Saturday.
"Complacency won't be a problem," said Hansen, who signed a new contract this year that will take him up to the 2019 World Cup.
"I always laugh when I see it written about me that I'm a great motivator.
"Well if the players aren't self-motivated then they shouldn't be playing Test rugby."
Hansen, though, expects another tough tussle not least because he says Schmidt has added more weapons to the traditional ones the Irish brought to the table before.
"He has got them playing. They are smarter," said Hansen.
"Ireland has always been passionate on and off the pitch and they're good people, I like their company.
"They like getting behind a cause.
"But Joe has improved their fitness and also honed them in the how, why and when...small words but very important ones.
"Now they are better at making decisions."
Original source: We are underdogs, says New Zealand coach Hansen