If he won on a first count by getting just over 50 per cent of the total vote including membership and unions but with low caucus support, National would repeatedly use it against him.
The caucus would look to be out of step with public opinion, which consistently rates Mr Cunliffe highly.
But second preferences could dramatically alter that perception.
More TV3 poll results last night suggested that Mr Cunliffe found favour with the public in terms of understanding the economy with 22 per cent against 12 per cent for Mr Robertson and Mr Jones.
More also thought he would be good in a crisis than the other two.
But more also thought Mr Cunliffe talked down to people and more thought he had more style than substance than the other two.
Mr Jones topped the poll with the question which of the three was more honest than most politicians, on 17.3 per cent followed by Mr Robertson on 16.3 per cent and Mr Cunliffe on 8.6 per cent.
The don't knows in the poll were huge, however, ranging from 47 per cent to 57 per cent for the various questions.
Mr Jones is clearly the underdog but he said last night he would be campaigning up until Saturday night.
"I joined this race not only to jolt our party, but to provide a genuine choice of someone who is quite different from the other two."
Asked if he was continuing to lobby his caucus colleagues, he said he had been calling and calling.
"I've been ringing them to the point that they see my name come up on the screen and they almost don't take my calls," he said last night." I'm making them hoha. I'm having to borrow other people's phones. In fact I was hoping to borrow Helen's [Clark] phone if she's still in the country and they might talk to me."
Meanwhile former Labour Finance Minister and Act founder Sir Roger Douglas says the two main contenders, Mr Cunliffe and Mr Robertson, have had been advancing policy "that would set New Zealand up to become another Spain or Greece."
"The Labour caucus I joined in 1969 understood perfectly well that a high income and standard of living are dependent upon high productivity and output," Sir Roger said.
"Per-person income depended on per capita output. Without an increase in real output, that is output adjusted for inflation, there can be no increase in income and no improvement in standard of living."
But policies such as raising taxes on the rich reduced work effort. Economic growth occurred only when more people earned more income which was why it was important to keep tax rates low.
"Clearly Robertson and Cunliffe are yet to learn 'there is no free lunch."'
The policy advocating a 'living wage' for all Government employees and raising the minimum wage would "increase the cost and risk of hiring workers."
"Why is that Robertson and Cunliffe act as if Government is a big Santa Claus?"
He said none of the three candidates had laid out a vision for New Zealand that would enable Labour to jump over National to dominate the middle ground of New Zealand politics.
Caucus support
Grant Robertson - 17
David Cunliffe - 12
Shane Jones - 5
- Estimates of support last night.
