National and Labour had been nearly neck and neck in opinion polls, with charismatic 37-year old Jacinda Ardern nearly single-handedly dragging Labour back into the race after taking over the party's leadership in August.
That means New Zealanders may wait days, even weeks, before knowing who their next leader will be as the different political parties negotiate with each other to form a coalition.
National, chasing a fourth term - a feat only achieved once before in New Zealand - struggled to find a way to counter a new, optimistic opponent.
In his speech late on Saturday night, after the vote count gave National a lead of more than 10 percentage points over Labour, English was reading directly from the May script: "We have the responsibility to deliver strong and stable government". New Zealand First has nine seats and Greens, which won 5.8 percent of the votes, have seven.
"I've called Bill and acknowledged that", Ardern told her supporters, adding she was planning conversations with both the Green and New Zealand First parties.
Labour saw a major surge after the July appointment of the 37-year-old leader but has fallen back slightly since.
National leader Bill English said he would start talking to NZ First in the next few days about forming a new government.
In contrast, English was bullish about his chances of securing a fourth-term government for National, a feat that has not been achieved in New Zealand for more than 50 years.
The nationalist New Zealand First Party had about 7.5 per cent of the vote so far, making it the likely kingmaker.More news: Facebook releasing 3000 Russian-bought adverts to Congress
More news: Pakistan, US agree to stay engaged after US Prez's tough talks
More news: Ryanair Pilots Reject Bonus Offer, Seek New Contracts Instead
Peters helped install a National-led government in 1996 in return for being made deputy prime minister.
Ms Ardern has been a game-shifter for the New Zealand Labour Party, appealing to the "young and urban", according to recently resigned leader of the party, Andrew Little.
The results secured 58 seats for National in parliament, and 45 for Labour.
"Only time will tell if this election will be any different, but I think if they turn out, that will really determine whether there's a change of government".
"There's conversations that need to be had and we're open to those", she said.
Citizens of New Zealand and Germany living in Australia will get to cast their ballots in their country's elections, with both nations heading to the polls this weekend.
"I would expect us to get a bit of a lift out of those special votes", said Ardern.
"We believe in laws and policies that support the mass majority of New Zealanders and not just a small elite".
She turned her flagging party's fortunes around in a matter of weeks but National, which has pinned its re-election bid on the economy's strong performance, has regained ground in recent opinion polls.