A defining vote in the race to replace Ban Ki-moon as the United Nations' chief will take place on October 5 in the Security Council.
The sixth secret ballot by the 15-member council will signal whether former Portuguese Prime Minister Antonio Guterres is likely to be the next secretary-general.
The vote will for the first time allow the candidates to see if they could be facing a veto from the five permanent Security Council members.
Guterres has come out on top in the five previous closed-door polls.
But amid a push for a woman to lead the world body for the first time, European Commissioner Kristalina Georgieva of Bulgaria was a last-minute entry a week ago.
Her candidacy could garner crucial support from Russia, which has said it would like to see a woman and an Eastern European take the top UN job.
The council is aiming to reach consensus on a replacement for Ban of South Korea, who will step down at the end of 2016 after two five-year terms.