McCullum said the team had decided, on a damp, green pitch, that attack was the best form of defence.
"On that wicket, the feedback from the boys was that at any stage a ball could have your name on it. I just tried to be as positive as I possibly could.
"It's not always going to come off, but we got a little bit of luck and we're sitting here firmly in the test."
He thought it might have been his day when he had "an almighty, filthy slog" at his second ball and it went over slips.
Add it to his 195 against Sri Lanka on Boxing Day 2014, test cricket's first day back in Christchurch after the 2011 earthquake, and McCullum is averaging 170 on Hagley Oval.
New Zealand were wobbling at 32 for three when he strode to the pitch. That McCullum was determined to go out on his terms, in his style, was apparent from that second ball.
It's not always the case, but the bare numbers tell a story. His 145 came off just 79 balls, with 21 fours and six sixes, the first of which took him to 101 and the world record for test sixes.
His one big letoff, on 39, had an appropriate touch about it.
A horror no-ball call at Wellington against New Zealand had a significant effect on that innings defeat. This time James Pattinson's over-step, after Mitchell Marsh had taken a spectacular one-handed catch at gully, proved costly for Australia.
From that point, McCullum struck 11 fours and two sixes in rushing to his century in a further 24 balls.
A McCullum innings of any length is bound to contain its share of skittish moments; the swing and miss, the top edge over the wicketkeeper, the fat edge through the slips, or the hoick skewed wider of mid-on than intended.
But they also contain a large proportion of outrageous, cleanly-struck shots. Today the drives were often thunderous, the pulls and hooks evading fielders and once again he showed that, when he's got the force with him, there are few to compare.
McCullum went to his hundred with 6, 4, 4, 4, in successive Josh Hazlewood deliveries, before lifting his arms in delight.
His often ginger back felt the crush of an Anderson hug as the crowd roared their delight. They were on their feet at 96, as if suddenly sensing history arriving at full pelt. A crash through extra cover completed the job.
In two hours, McCullum did three things: he hauled his team back to their feet in a match they have to win to square the series; enabled him to farewell New Zealand cricket on his terms; and gave his adopted city something to remember for the second time.
McCullum had talked about the touch of romance about signing off at home. Today he did it with as spectacular flourish as could be imagined.
His 54 ball beat the previous record held by Pakistan's Misbah-ul-Haq and West Indian Sir Viv Richards.
"Viv was my idol growing up so it's nice to go past him on this occasion but he was a cracking player, an incredible cricketer," McCullum said. "I'm almost embarrassed."
He shouldn't be.
- By David Leggat in Christchurch
