Observers and other officials in Kabul yesterday were worried both candidates are setting the stage to complain about fraud and refuse to accept defeat should the outcome of the vote be close.
The United Nations is urging the candidates, former Northern Alliance leader Abdullah Abdullah and former finance minister Ashraf Ghani, to honour the election procedures, in the tallying of votes.
If successful, the vote will mark the country's first democratic transfer of power in its history.
The winner will succeed President Hamid Karzai.
Mr Abdullah, who dropped out of the 2009 run-off against the president, has spent five years in the opposition.
His opponent, Mr Ghani, is a former World Bank economist.