Lotto would not reveal further details, citing privacy reasons, but said "a bit of luck" was needed.
"He thought we were real estate agents," said Emilia Mazur, Lotto's corporate communications manager.
"Once we explained who we were and why we were there - that we believed he had bought the winning ticket - he was initially dubious.
"Not as to who we were, but as to believing that he had the winning ticket. He had heard from a workmate that somebody else had won, so he hadn't bothered to check his ticket."
Ms Mazur, who went with Lotto's chief operating officer Chris Lyman to deliver the news, said once further details were provided the news started to register.
The man has chosen to remain anonymous but said he was "really, really chuffed" to be found.
"I can just live on the interest - I don't want to work until I'm 65, and now I don't have to."
The $22.6 million lottery prize is the largest in the South Island, and the man said he was staying put.
"I love Christchurch and I wouldn't want to live anywhere else. Maybe now I can build the house of my dreams here."
Mr Lyman said big prizes are usually claimed within days. "The prize had gone unclaimed for more than three weeks and we were worried someone may have lost the ticket or forgotten they'd bought it."
Bearers of good news
*Man thought real estate agents were at the door when Lotto officials arrived.
*Hadn't bothered to check ticket after workmate told him the prize had been claimed.
*Paid cash for ticket, so Lotto and staff at Pak'nSave used video footage to work out who he was.