Another major rival to Afghanistan's interim president, Hamid Karzai, has pulled out of a boycott of last Saturday's election.
General Dostum on the campaign trail
Warlord General Abdul Rashid Dostum now says that he is instead supporting a United Nations investigation into complaints about the voting.
General Dostum was one of 15 candidates who called for the boycott.
It overshadowed what is widely viewed as being a hugely successful first election for Afghanistan.
Officials say the counting of ballots will not now begin before Thursday.
A UN-appointed investigation panel has given candidates another 48 hours to make complaints, extending the deadline until 1800 local time on 14 October.
But one of the members of the panel, Craig Jenness, indicated that it might be possible to start the count after isolating ballot boxes from polling stations mentioned in complaints received so far.
Last big challenger
The candidates called the boycott after problems emerged with indelible ink designed to prevent fraud.
But it started crumbling on Sunday.
The key moment was when Yunus Qanuni, the most important rival to President Karzai, backed down, saying he wanted a UN investigation into his concerns on polling day instead.
Two people have already been appointed to the UN investigation panel, and a third is currently being identified.
General Dostum, the veteran Uzbek strongman, is the last major challenger to Mr Karzai to come on board for the investigation.
But his spokesman says he will still make complaints about the way Saturday's vote was conducted, despite missing the initial deadline for doing so.
Since Saturday's election, candidates like General Dostum have been under intense pressure to abandon their boycott.
Negotiations have involved Western diplomats as well as Afghan figures.
But the BBC's Andrew North in Kabul says that many believe another factor in changing minds has been widespread anger among ordinary Afghans at what they see as candidates obstructing a popular process for short-term political gain.
Speaking at a news conference in Kabul, Craig Jenness said 43 complaints had been received from the 18 candidates so far, of which 37 had been reviewed.
Ballot boxes from 10 polling stations had been isolated as a result, he said.
Meanwhile, eight people who were stranded for 24 hours when a helicopter sent to pick up ballot boxes crashed in mountains in northern Badakhshan province have been rescued, the UN said.
Spokesman Manoel de Almeida e Silva said the rescue helicopter would return later to pick up the boxes.
In Kabul, the head of US forces in Afghanistan, Lieutenant-General David Barno, has called the elections "the end of more than two decades of the rule of the gun".
"[The election] confirms the bright hope of all the Afghan people in a democratic future centred on the rule of law," he said.
However, General Barno said US troops would remain in the country for the foreseeable future.