The Budget increased some welfare payments by $25, while also scrapping a $1000 Kiwisaver payment and introducing a levy at the border.
It also introduced new residential housing measures including a tax on capital gains, stricter tax requirements for foreign buyers, and plans to free up state-owned land in Auckland for development.
The poll was also the first by One News since Mr Key was accused of harassing an Auckland waitress by repeatedly pulling her ponytail.
It appeared to show that his popularity has not dropped as a result of the incident, which generated headlines around the world and could lead to legal action against him.
In the preferred Prime Minister poll, John Key rose 2 points to 44 per cent.
Leader of the Opposition Andrew Little's support fell two points to 9 per cent, and he was now level in the popularity stakes with New Zealand First leader Winston Peters.
In the aftermath of the Budget, Mr Little said it was unfair that people who kept working past age 65 received a pension.
He later clarified that he was not in favour of means testing for superannuation.
The proportion of undecided voters rose 4 points to 13 per cent in the poll, which had margin of error of 3.1 per cent.