A decision by Labour's Hutt South MP Trevor Mallard to stand on the list only next election makes it more likely the seat will fall to National.
Mallard has had a strong personal following in the seat, having held it since 1993.
But in the 2014 election, National's young candidate Chris Bishop reduced Mallard's majority to just 709, from 4825 in 2011.
Mallard would also have picked up votes from local Green candidate and list MP at the time Holly Walker, who was retiring from politics.
The greater indication of where the seat could head in next year's election in in the party vote: National overwhelmingly won the party vote with 17,648, well ahead of Labour on 10,903.