One poll does not make a trend. And the Herald-DigiPoll survey flattered Labour earlier this year, only to deceive in a subsequent poll.
But the results of the latest poll are understood to have been replicated in Labour's private polling.
National's pollsters apparently also recorded a marked drop in support for the party around the same time as the Herald-DigiPoll surveyors were asking their questions, although the numbers are said to have since bounced back in National's favour.
It will take a major public poll to confirm either that it is business as usual or that things really are on the change.
What is different with respect to current political atmospherics is that the phony war between the two major parties which resulted from Cunliffe's election coinciding with an extended bout of official overseas travel by the Prime Minister is well and truly over.
To show he is still boss, Key rode into town this week with all guns blazing.
For the first time outside the parliamentary chamber, he had Cunliffe very much in his sights.
The Prime Minister claimed he had information that Labour's leader had privately told SkyCity's management that although Labour's official line was that the pokies-for-convention-centre deal was shonky, Labour would not accede to the wishes of the Greens and rip up SkyCity's contract with the Crown.
Facing his first real test as leader, Cunliffe vigorously denied the charge before deliberately ducking and fudging to such an extent that confused reporters drew completely different conclusions about where Labour stands on the matter.
This is not a tactic that Cunliffe can resort to using too often.
Key will keep up the pressure. He knows Cunliffe is in a very difficult position.
On the one hand, there are those in Labour who would seek to nobble SkyCity as a matter of principle.
Others take the view that an international convention centre means jobs, and Labour's supporters in lower socio-economic areas would take a dim view of the party kiboshing the project.
Moreover Labour cannot afford to be seen to be ripping up contractual obligations, thereby destroying its credibility with international investors and the moderate voters Cunliffe must win back from National to gain power.
Here lies Key's wider strategy. Labour needs to show it can work with the Greens to convince people that a centre-left government is a workable proposition.
At the same time, Labour needs to create some distance between itself and the Greens to avoid accusations it is in their pocket.
National will seek to exploit that dilemma by trying to drive a wedge between Labour and the Greens so voters will realise the two parties are fundamentally incompatible.
But National has to be smart when it comes to scaremongering. The strategy was used to poor effect when National was on the defensive this week after its less-than-triumphant partial float of Meridian Energy.
Ministers blamed the small number of investors signing up for shares on "economic sabotage" by Labour and the Greens in the form of their plans to "nationalise" the wholesale electricity market.
It was far more the case that the float was sabotaged by those same ministers setting too high a price for shares in the earlier float of 49 per cent of Mighty River Power.
Once burned, investors were twice shy about Meridian.
National has also tried to get off the back foot by suggesting that if Labour and the Greens were really serious about nullifying the partial privatisation programme, they would be willing to borrow money from overseas to buy back the assets.
Neither party has been silly enough to fall into the trap of agreeing. Both can be confident that voters do not expect political parties to become hostage to decisions made by previous governments. Once the assets are sold, they are sold.
Much the same logic applies to Labour's attempts to besmirch Key for not having disciplined John Banks or cut him adrift. Voters might not like it either, but they understand why the Prime Minister has to keep Banks on board.
The Prime Minister also let rip at Winston Peters this week with an astonishing declaration that you would get more sense out of the Mad Hatter's Tea Party than New Zealand First.
This is a puzzling move, as National might need Peters if it is to govern after next year's election.
Such an insult is not something Peters is likely to forget in a hurry, but Key has made no secret of his antipathy towards having to work with New Zealand First's leader. Despite having seemingly little room to manoeuvre, he is clearly developing a strategy to shut Peters out.
He is punting that a good portion of those who voted for New Zealand First in 2011 will switch back to Labour next year.
He also clearly feels Peters could then be marginalised on the right by Colin Craig's Conservatives, who are not that far removed from New Zealand First's ideology.
That would require giving Craig a free run in the new Auckland electorate created by population gains in the region.
National supporters would be instructed to give their electorate vote to him, presuming he was the candidate. The Conservatives would repeat what Act has done in Epsom, but with a real chance of bringing more than one MP into Parliament.
A vote for New Zealand First would be painted as being, at best, a wasted vote, and, at worst, a vote for Labour.
The message from Key this week is crystal clear - any changes in the landscape are going to be at his behest, not that of others.
