By Alexis Akwagyiram and Tim Cocks
LAGOS, (Reuters) - The final stage of Nigeria's election will begin on Saturday with state governorship polls, two weeks after a presidential vote saw an incumbent leader unseated at the ballot box for the first time.
The 36 governors are among the most powerful politicians in Africa's biggest oil producer and top economy, controlling budgets larger than those of small African nations and wielding influence that can decide who goes on presidential tickets.
Voting starts at 8 a.m.
With so much at stake, candidates in past polls have often played dirty, snatching ballot boxes, manipulating voter turn-out and engaging in thuggery and intimidation.
Muhammadu Buhari beat President Goodluck Jonathan last month with 15.4 million votes against 13.3 million, in a vote that was considered free and less violent than past polls.
Yet for many Nigerians, who their governor is matters more than who sits in the faraway capital Abuja.
"It will be slightly dirtier, a bit rougher in some places. Locals are more invested in the process around them. The federal government is like a no man's land," said Folarin Gbadebo-Smith, head of Nigeria's Centre for Public Policy Alternatives.
Legislative polls also shifted power away from the People's Democratic Party (PDP), which has run Nigeria since the end of military rule in 1999, to the All Progressives Congress (APC). It left the APC with a majority in both houses.
The APC is seeking to build on its gains, while the PDP will hope it can claw back power, especially in two battlegrounds -- the megacity of Lagos, the country's economic engine generating up to a third of its GDP, and the oil hub of Rivers.
Both are currently APC, Rivers only because its sitting governor defected. Both could be magnets for trouble, as could the northern swing state of Kaduna, which saw hundreds killed in sectarian violence after the 2011 presidential election.
In all 30 states hold elections, with six sitting them out since they had by-elections in the last few years.
"The Nigerian army has directed all units to remain vigilant... to prevent any attempt to endanger the lives of Nigerians," the army said in a statement on Friday.
Biometric voting cards that were used for the first time in last month's poll and helped prevent fraudulent practices like multiple voting or ballot box stuffing, will again be used.
"The card reader is the only way that rigging on a large scale can be stopped in this country," Abubakar Momoh, of the Independent National Electoral Commission (INEC) told Reuters.
Outgoing APC Lagos governor Babatunde Fashola is credited with transforming a megacity of some 21 million and an economy twice the size of Kenya's through infrastructure projects, although he has also been criticized for slum clearance.
(Additional reporting by Oludare Mayowa in Lagos and Lanre Ola in Maiduguri; Editing by Angus MacSwan)