Cape Verde President Pedro Pires has declared victory in Sunday's election.
Pedro Pires was the first president after independence in 1975
Final results have not been announced but his cheering supporters have taken to the streets.
"It's a great honour to deserve the confidence of Cape Verdeans," said Mr Pires, 71, who defeated his rival Carlos Veiga by just 12 votes in 2001.
With a majority of the ballots counted, Mr Pires had 50.1% of the vote, with Mr Veiga trailing slightly with 49.9%. Mr Veiga has not conceded defeat.
Economic development and the reduction of poverty dominated the election campaign.
Cape Verde has a high unemployment and crime rate, but is also seen as politically stable with an emerging prosperity.
Both leading candidates - who would rule for the next five years - have pledged to promote faster economic growth and tackle crime.
Mr Pires' ruling African Party for the Independence of Cape Verde (PAICV) won January's parliamentary elections with 52% of the vote.
Appeal to voters
Voting in Cidade de Praia, Mr Pires called on all Cape Verdeans "to take part in this very important decision".
Mr Veiga, who accused the opposition of fraud in the 2001 election, said earlier: "I trust I will win, and I expect elections to go smoothly and in a transparent way."
Carlos Veiga lost by 17 votes in the last presidential election
The preliminary results were announced after votes in 1,005 of the 1,184 polling stations on the 10 Cape Verde islands had been counted.
The two leading candidates have dominated politics in the tiny West African archipelago since it won independence from Portugal in 1975.
The PAICV first came to power under a one-party system after independence, with Mr Pires, as Cape Verde's first prime minister.
Mr Veiga's Movement for Democracy (MpD) won the first multi-party elections in 1990.
The 56-year-old Mr Veiga served as premier for the next 10 years until the PAICV regained power in 2001.
About 325,000 Cape Verde citizens were registered to vote. Of these, about 20% live abroad - mostly in Portugal.