Nigeria's former anti-corruption chief Nuhu Ribadu has been chosen as the opposition Action Congress candidate for April's presidential polls.
Two other contenders stepped aside to allow Mr Ribadu to win unchallenged.
His entry into the presidential race come hours after Nigerian President Goodluck Jonathan won the ruling People's Democratic Party primary.
The PDP candidate has won every poll since the end of military rule in 1999, despite allegations of fraud.
Mr Ribadu came to prominence as head of Nigeria's Economic and Financial Crimes Commission.
While in office he prosecuted several high-profile politicians, before being sidelined after the elections in 2007.
He returned from exile in June 2010, after saying he had fled because attempts had been made on his life.