President Goodluck Jonathan took an unassailable lead as votes were tallied from around Nigeria, despite a strong showing by rival Muhammadu Buhari in his mainly-Muslim strongholds.
Mr Buhari was hoping to at least force a second round against Jonathan, but that looked impossible with a Reuters tally of results from 30 of 36 states across Africa's most populous nation showing Jonathan on 20.3 million votes to 10.4 million for Buhari.
There were not enough registered voters in the remaining states for Buhari to make up the difference.
Observers called the election the fairest for decades in Nigeria, where rigged polls have been the norm, although there were still suspicions of malpractice in some districts.
Jonathan's officials said there would be no victory claim until results were announced by the Independent National Electoral Commission.
The president did particularly well in his predominantly Christian south, while Buhari swept many northern states in the country of 150 million people.
To avoid a run-off, the winner must get a simple majority and at least a quarter of the vote in 24 of the 36 states. Jonathan already had that margin in enough states.
An outright win for Jonathan could ease worries over potential disruptions to crude exports from Africa's biggest oil producer and lift local financial markets awaiting the end of a series of elections.
