Portugal's former PM Antonio Guterres topped the first poll, AP reported on Friday, and Slovenia's former president Danilo Turk finished second.
Three candidates tied for third, then Clark secured fourth spot.
The Security Council is expected to host further straw polls between now and possibly early September, before making its recommendation to the UN General Assembly by October.
The assembly will then decide whether to choose the recommended candidate.
A recommendation has never been ignored by the assembly in the UN's history.
Clark put in a strong performance during a debate between candidates last week, the first of its kind to be internationally broadcast. She began by dismissing the idea that the job should go to an Eastern European candidate, in line with the organisation's geographic rotation policy. Noting that the UN's electoral system put New Zealand in with western European countries, she said: "My little country is from the South Pacific and it has never had a Secretary-General either. When we look at the scale of the challenges the world is facing, we need a global search for the best talent."
She promoted her long leadership experience and ability to make "a lot of hard calls".
An unscientific poll by Al Jazeera, which hosted the event, ranked Clark and Costa Rican candidate Christiana Figueres as the debate's best performers.
Ban, the eighth Secretary-General of the United Nations, took office on January 1, 2007 and will finish his two terms, the traditional length of time in the top job, at the end of 2016.
The candidates
Natalia Gherman Moldova, Former deputy Prime Minister and Minister of Foreign Affairs.
Antonio Guterres Former UN High Commissioner for Refugees and former PM of Portugal.
Vuk Jeremia President, Centre for International Relations and Sustainable Development, former Minister of Foreign Affairs in Serbia.
Srgjan Kerim Macedonia, former Foreign Minister and former President of UN General Assembly.
Miroslav Lajcak Minister of Foreign and European Affairs in Slovakia.
Igor Luksic Montenegro's Deputy Prime Minister and Minister of Foreign Affairs.
Susana Malcorra Argentina, Minister of Foreign Affairs.
Vesna Pusic Croatian Deputy Prime Minister and Minister of Foreign Affairs.
Danilo Turk Chair of the Global Fairness Initiative and former President of Slovenia.