Ghana's opposition asks top court to overturn poll results ACCRA (Reuters) - Ghana's main opposition party on Friday asked the West African nation's top court to overturn the result of a December 7 presidential election won by incumbent President John Dramani Mahama over what the party's leader called irregularities. The poll, which passed peacefully despite technical problems that forced voting into a second day, was seen as a test of stability for one of Africa's most mature democracies and fastest growing economies. New Patriotic Party (NPP) leader Nana Akufo-Addo, who came second in the closely fought contest that observers said appeared fair, said his party had evidence to show there were enough irregularities to affect the outcome. "A few minutes ago a petition was filed at the registry of the Supreme Court, challenging the validity of the result of the presidential election," Akufo-Addo told a news conference in Accra. This case is not about candidate Mahama or candidate Akufo-Addo. There is a much more important issue at stake which goes to the heart of our democracy and the future of our nation," he said. The Electoral Commission declared Mahama winner with 50.7 percent of valid ballots to Akufo-Addo's 47.7 percent. After the poll, Mahama urged Akufo-Addo and other opposition figures to join him "as partners" in improving Ghana, but said his rivals had a right to take their grievances to court. Mahama, who initially took over from former President John Atta Mills after his death in July, is expected to be sworn in on January 7 to begin a full four-year mandate. The gold, cocoa and oil exporting country has managed more than 30 years of democratic transfers of power, making it an anomaly in West Africa's so called "coup belt" of countries plagued by instability. Reporting by Kwasi Kpodo; Editing by Richard Valdmanis and Roger Atwood