Hansen is stepping back into a coaching role with the World XV that will play the Barbarians on May 28 at Twickenham.
While Ireland deserved their No1 ranking because of the great year they had enjoyed, they face a more significant hurdle if they are to cap that with their first World Cup win.
"Ireland was good throughout the Six Nations. In the final game, they started a bit shaky, and England rattled them a bit. But, once the red card came, it was game over, and they were good enough to take advantage of it.
"They're going well, ranked No1 in the world, and they've had a great year so far.
"Every time a team is No1 in the world, you've got to consider them a World Cup contender. But it's a tough tournament to win, and they were No1 going into the last one, weren't they?
"So, they've seemed to struggle a little bit at World Cups – if it was the All Blacks, they'd probably be called 'chokers'."
However, under coach Andy Farrell Ireland had come a long way. They were a very good side and would be a contender.
"But, they'll have to overcome the pressure of not having gone past the quarterfinals before, and there'll be a lot of pressure involved in that.
"If they get through to the semifinals, then they're in new territory.
"That's something they'll have to deal with that they've never dealt with before, and it's always hard to deal with something you haven't dealt with before."
The All Blacks, by comparison, were flying under the radar as the attention has all been on Ireland and tournament hosts France.
But Hansen warned critics to write off the All Blacks at their peril.
"Beware an All Blacks that's not considered 'good enough' to be winners of the World Cup – because that can come back and bite you."
Hansen said he looked forward to the World XV fixture against the Eddie Jones-coached Barbarians. He expected a high-skilled game as both sides entered the spirit of a traditional Barbarians game of open and flowing rugby.
