The governorship election in southwest Nigeria's Osun state ended in a stalemate on Sunday when the nation's electoral body failed to declare a clear winner.
Tensions rose at the INEC's collating centre in Osogbo on Sunday as supporters of the leading parties waited in vain for the official announcement of the results before it was announced a runoff was required.
Although 48 candidates from different political parties contested Saturday's election, the leading candidates were Gboyega Oyetola from President Muhammadu Buhari's ruling All Progressives Congress (APC) and Ademola Adeleke of the main opposition Peoples Democratic Party (PDP).
Olusegun Agbaje, the Independent National Electoral Commission (INEC) chief in Osun told reporters the election was inconclusive because "the number of cancelled votes is higher than the margin between the two top candidates."
A run off between Oyetola and Adeleke is expected to be held on September 27.
An unofficial tally had shown the PDP's flagbearer leading his APC counterpart by some 350 votes, while the voided votes were more than 1 000.
Under the country's electoral law, no winner will emerge if the margin of victory is less than cancelled votes.
The winner of Saturday's poll was expected to take over from APC Governor Rauf Aregbesola, who is stepping down after two four-year terms, the legal maximum.
Adeleke who is nicknamed "the dancing senator" because of his penchant for dancing in the public, is an uncle of Afropop star Davido, whose real name is David Adedeji Adeleke.
Davido had joined the political trail to campaign for his uncle, drawing huge crowds as he ditched out some of his popular tunes.
The PDP candidate is a scion of the prominent and wealthy Adeleke political dynasty in Ede, some 20km from Osogbo, the capital.
Although there were widespread concerns about vote-buying, intimidation and logistics problems, the vote was generally adjudged free, fair and violence-free by local and foreign observers who monitored the exercise.
The governorship election in neighbouring Ekiti in July was characterised by allegations of vote-buying by the leading political parties.
Police, however, said three suspects were arrested for an alleged vote-buying in Osun on Saturday and would be prosecuted at the end of investigation.
The election is the final major electoral test before Nigerians vote for a new president, parliament, governors and state legislatures in February and March next year.
Buhari who came to power in 2015, faces a formidable challenge from an array of opposition candidates from PDP, including former vice president Atiku Abubakar and Senate president Bukola Saraki.
The 75-year-old retired general who headed a military regime in the 1980s is under pressure to step down because of failing health after spending several months in London last year treating an undisclosed ailment.
He has also come under fire over the management of the economy and growing insecurity problems, including Boko Haram insurgency in the northeast, long-running farmer-herder clashes in the centre and militancy and kidnapping in the south.