Former Portugal prime minister and UN high commissioner for refugees out in front after third ballot vote to choose Ban Ki-moon’s successor

Portugal’s former prime minister, Antonio Guterres, has consolidated a strong lead in the race to become the next United Nations secretary general, after a third security council secret ballot on Monday.

Diplomats said that only a decisive stand by Russia, which has argued that the job should go to an eastern European, could now stop Guterres succeeding Ban Ki-moon in the UN’s top job. A fourth straw poll is expected in September in the hope that a consensus forms around a winner by October.

In a succession of straw polls by secret ballot, the 15 security council members vote whether to encourage, discourage or express no opinion about a candidate. Results of Monday’s poll supplied by diplomats showed 11 members voted to “encourage” Guterres, who served as the UN high commissioner for refugees for a decade.

That was the same level of support as the previous vote, on 5 August, but the number of discourage votes rose from two to three, with just one voicing no opinion.

Miroslav Lajcak, the Slovak foreign minister, was a surprise runner-up, rising from 10th place out of 11 contenders earlier this month. In joint third position were Vuk Jeremic, a former Serbian foreign minister, and Irina Bokova, a former Bulgarian foreign minister and director-general of Unesco, the UN education and cultural organisation, and the last serious hope for those who wanted a woman to take the world’s top diplomatic job for the first time.

“This really widens the gap in the race. It shows Guterres’s lead has stabilised,” a diplomat at the UN said. There was widespread speculation that either Russia or a Russian ally on the council had switched from no opinion to an anti-Guterres vote.

“The real question is whether this discourage vote is tactical, in order to exact a price for Russian agreement, or whether it is substantial and they are saying: we don’t want him,” the diplomat said.

Russia and the four other permanent council members – the US, UK, France and China – all have the power to block a candidacy. Although this secretary general race has been far more open than previous contests, the winner will still have to be agreed by the five permanent members, as before.

Lajcak’s dramatic rise makes him a feasible compromise candidate if Russia remains adamant on Guterres, though he received five discourage votes. It is not known whether there were permanent members among those five votes.

A number of candidates who fared poorly in the latest straw poll will now be under pressure to drop out of the race. They include Moldova’s former foreign minister Natalia Gherman, and the UN’s former climate chief, Christiana Figueres. Helen Clark, an early favouritebacked by several western capitals, got eight discourage votes in the against only five backing her. Diplomats said she would now face a tough decision on whether to stay in the race.

Matthew Rycroft, Britain’s ambassador to the UN, urged low-scoring candidates to pull out, to help winnow the field in the last stage of the race.

“I would encourage them to look at are they going to get to nine positive votes and no vetoes. And if they are, then great – they should stay in the race,” Rycroft said before Monday’s vote, adding that “if that’s a long way off” they should follow the example of earlier contenders who had withdrawn.