Guinea Bissau's presidential poll winner, former military ruler Joao Bernardo Vieira, has said he will steer the country in "the right direction".
Mr Vieira first came to power in a coup in 1980
He praised his rival Malam Bacai Sanha and calling him a democrat and said he hoped he would help unify the country.
Earlier, Mr Sanha's spokesman said the polls were marred by fraud and demanded a recount in two constituencies.
There were reports of clashes between rival supporters in the capital, Bissau, after the results came out.
Mr Vieira, known as Nino, came to power in a coup and ruled for 19 years until overthrown in 1999 by the armed forces.
But he returned from exile this year to run for office again in the election intended to end years of coups and political instability.
'Gift of God'
"From today, Guinea-Bissau will change in the right direction," AFP news agency quotes Mr Vieira as saying after the provisional results from Sunday's presidential run-off were announced.
1980: Seized power in a coup
1994: Won elections
1999: Ousted in a coup
2005: Wins run-off with 55.75%
Support base: Urban youth
He took 55% of the vote compared to 44% gained by Mr Sanha, the electoral commission said.
"I congratulate my adversary, Malam Bacai Sanha, a democrat," he added.
"I hope that his experience and talent will serve for the unification, pacification and development of our country."
During his campaign, Mr Vieira described himself as a gift of God to the people of Guinea-Bissau coming back to lead them to prosperity.
Both candidates had previously promised to respect the outcome of the election but a spokesman for Mr Sanha, Desejado Lima Da Costa, said there had been fraud in two places, including the capital, Bissau, which must be addressed first.
He also criticised the head of the electoral commission for refusing requests for a recount.
'Calm and organised'
Mr Sanha gained the most votes in the first round of voting.
European monitors said voting was "calm and organised".
The BBC's Ebrima Sillah, who was in Bissau for the election, says people there are waiting to see if the military will this time respect the democratic choice.
Guinea-Bissau won independence from Portugal in 1974, but has had a chequered history of coups and military dictatorships ever since.
Mr Sanha's PAIGC party ruled the country from independence until it was overthrown by Mr Vieira in 1980.
Mr Vieira then won presidential polls in 1994, but was himself overthrown in 1999 as the country descended into civil war.