Labour, the Greens, Mana and New Zealand First will all oppose any asset sales from Opposition despite National increasing its vote to 47.99% - and some commentators have suggested National doesn't have a mandate.
Many polls before Saturday showed strong public opposition to sales.
"I utterly reject that," Mr Key said, in a clear indication of his intention to forge ahead with the policy.
"An election campaign is all about the contest of ideas. One of the most hotly debated issue was the mixed ownership model and the contrast between that and increasing New Zealand's debt. And in Government we lifted our party vote."
He said he acknowledged some New Zealanders were anxious about the mixed ownership model.
"But I think we got a mandate."
Mr Key said he expected to run a Government very similar to the one he had run in the first term.
"By that what I mean is I expect it be a balanced Government. I expect it to be moderate. We will be working with other parties but we will be very focused on those issues that dominated the campaign period."
That included the partial asset sales, welfare reform, and returning the Government's book to surplus by 2014-15, if not before.
The National caucus will meet in Wellington tomorrow, where it will farewell list MP Paul Quinn, who lost his place on the list.
"We are disappointed for him," Mr Key said.
"It seems a cruel result given that we have gone up to 60 seats [from 58], but that is the quirkiness of MMP.
His list place was 55 compared with 48 last election.
Mr Key indicated Mr Quinn had been a victim of the party's list ranking committee that sometimes refreshed the list to get greater ethnic diversity.
"For instance Jian Yang, the new Chinese candidate, came in [at number 36]. By the time you've pretty much ranked the cabinet and the caucus and things, it was always going to be tight."
The caucus will number 60 and with such a large number to manage, Mr Key is considering recommending three whips instead of the current two.
One of the high points of the National result was the Nikki Kaye keeping Auckland Central against Labour's campaign by Jacinda Ardern and Nicky Wagner possibly winning Christchurch Central, where the vote is tied.
Mr Key said the Christchurch vote, which saw National outstrip Labour on the party vote in every electorate, was an endorsement of National's response to the earthquakes.
"I always thought we had a lot of goodwill in Christchurch. I am constantly stopped in the street and thanked for the support in Christchurch."
While there were a series of challenges that needed to be resolved from insurance through to EQC "I think everyone who is living there is quite conscious of the enormity of the challenge".
It also reflected the work Earthquake Recovery Minister Gerry Brownlee had done.
"He has copped a lot of flak along the way, but that is because people have genuine frustrations ... but for the vast bulk of Cantabrians they can see he is doing everything he can."
Mr Key also said it was also remarkable National won the party vote in Dunedin South.
