John Key has used his friendship with Barack Obama to get Helen Clark vital face time with him.
The Prime Minister introduced Ms Clark to the US President on the sidelines of United Nations.
Mr Key says he called Ms Clark over to Mr Obama during a private event where she used her face time to push hard for the Secretary-General role.
"We were all there and the three of us had a bit of a chat. Then she wandered off - she was working the meeting pretty hard," Mr Key says.
The United States has a veto power over the Secretary-General so its support is crucial.
Earlier on Wednesday, Mr Key addressed the United Nations General Assembly where he also pushed for Ms Clark as the best candidate for the top job.