Mr Key has tried to stifle his rival's attempts to claim underdog status, saying Mr Cunliffe should not be underestimated: Mr Cunliffe had been in Parliament longer than Mr Key and was an experienced debater.
In an apparent attempt to psyche out Mr Cunliffe, Mr Key spent the morning meeting shoppers at Albany before making two health announcement, while Mr Cunliffe locked himself away all day to prepare for it. Key added that he hoped to get in some time shooting hoops with son Max that afternoon, but would put in a bit of time for prep.
Mr Key denied he was playing mental games with his apparently relaxed attitude, and said he had campaigned on debate days even when he was Leader of the Opposition in 2008.
"It's different strokes for different folks. But I'm expecting a tough debate tonight. David Cunliffe has been in Parliament longer than me, he's been a Minister, everybody knows he's a good debater. I haven't taken him lightly."
Both also admitted they had done some practice runs with stand-ins for their rival - but neither would say who those stand-ins were.
• POLL PRESSURE: Labour sinks lower
• LEADERS' DEBATE: Touch that dial
• JOHN ARMSTRONG: Cunliffe must take charge or it's all over
• JULIE CHRISTIE: Muck-raking will draw a backlash
The performance of the moderator, Mike Hosking, is likely to get just as much scrutiny as the two leaders. Mr Cunliffe had initially objected to Mr Hosking as the moderator because he had spoken favourably about Mr Key and National in the past.
Although rough politics has dominated the campaign, Mr Cunliffe said he intended to keep the debate clean, saying his primary aim was to show New Zealanders he was ready to be Prime Minister. "I don't think Kiwis would appreciate some kind of headbutting contest between the two of us."
Although Cam Slater's return to New Zealand and police complaint risked raising Dirty Politics again, Mr Key said voters were more interested in the economy, health and law and order than Mr Slater.
"I suspect the million or so viewers that watch that will be really interested in the things that drive this country and the changes we make. What a blogger does or doesn't do is not likely to be top of mind."
He said the ability to set out a plan was what could change votes in such a debate, not just "a zinging one-liner" despite flooring Goff in 2011 with his 'show me the money' line.
"The 'show me the money' came out of the top of my head in a debate about Labour's inability to get the numbers to add up. Three years later and the numbers still don't add up so maybe I can just use the same one-liner."
As for superstition, Mr Key is likely to wear his lucky cufflinks tonight. Mr Cunliffe said he did not have any similar superstitions, but would spend a quiet few minutes alone just before the debate. Asked if he would use that to pray, he said "maybe".
HOW THEY STACK UP
DAVID CUNLIFFE
Age: 51
Time as leader: 11 months, so it's his first debate as leader
Previous opponents: Finance Minister Bill English in 2011 campaign Primary goal: Look like a Prime Minister in waiting
JOHN KEY
Age: 53
Time as leader: Seven years, Prime Minister since 2008
Previous opponents: Helen Clark, Phil Goff
Primary goal: Get rid of the dirty politics shadow and try to reassert himself as someone to be trusted.
