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Mr Cunliffe has seen his party's support, and his own, slip in recent opinion polls but lately his personal stakes have been slowly increasing.
Text support for the One News Leader Debate, moderated by Mike Hosking, was overwhelming in favour of Mr Key.
However, Mr Cunliffe remained on message throughout the debate, despite getting flustered during the session on overseas land sales and not answering some questions.
For his part, Mr Key stood relaxed with one hand in his pocket, showing his grasp of not only National's policies but also a good understanding of what Labour and the Green Party were offering.
But, as in Dunedin two weeks ago, Mr Key's face told a different story - one of stress or pressure.
Mr Cunliffe quipped the Prime Minister should take ownership of his own policies, rather than interpret Labour policy.
Undoubtedly, much will be made of Mr Cunliffe's smile which was plastered on to his face last night, but the Labour leader proved sharp with some one-liners, usually the forte of Mr Key.
Mr Cunliffe revived a previous political quote about a ''block of cheese tax cut''.
Mr Cunliffe was also generous but cutting with a particular comment regarding the average wage and tax cuts.
''No-one is criticising John for getting New Zealand through the worst of the crisis, but people are asking where to from here and where's my share?''
The debate started with questions on dirty politics and how the respective leaders rated the campaign so far for dirty tactics.
Mr Key rated it a five, turning the issue back again to a left-wing conspiracy.
Mr Cunliffe rated it a six and said unsavoury ministerial behaviour would not be tolerated if he was prime minister.
After a relatively gentle start, the debate deteriorated in the second section, when Mr Cunliffe could not answer how 10,000 houses a year would be built without skilled builders.
Mr Hosking pushed hard to find where Labour's KiwiBuild houses worth $360,000 would be built, claiming Labour could not defy the market and that the policy would turn parts of Auckland into ghettos or dumps.
Mr Key was not asked the same question and was left to criticise Labour's so-called ''wish list''.
Mr Key also caught Mr Cunliffe out on capital gains tax when he pointed out farms and businesses would be be included in any new tax and the Lochinver Station, the subject of much debate about prospective Chinese ownership, would be worthless under Labour's policy.
Mr Key had the stronger finish of the debate, and that point will stick in the minds of voters.
Mr Hosking asked both men to rate their performance and that of their opponent.
Mr Key said he was not there to rate David Cunliffe, as he was not a political commentator, saying the political contest was about ideas and policy.
Mr Cunliffe hoped he was speaking to New Zealanders about things that mattered to them and said he always respected Mr Key but they had different ideas.
''He is the past, we are the future,'' Mr Cunliffe said.