Initial results showed Nasheed, who was rousted from office 18 months ago, unofficially received 45 percent of the votes cast, China's Xinhua News Agency reported.
Nasheed's opponent in the second round of voting Sept. 28 had yet to be determined, Xinhua said, with former President Abdul Gayoom's half-brother Member of Parliament Abdulla Yameen ahead of businessman Gasim Ibrahim 25.5 percent to 24 percent in unofficial results Saturday.
Incumbent Mohamed Waheed Hassan Manik, who became president after Nasheed was ousted in February 2012, received just 5.3 percent.
"At this stage none of the candidates have polled more than 50 percent," Fuad Thaufeeq, head of the Elections Commission, told reporters Saturday night. "The elections were held in a very peaceful manner but in every election there are complaints and there have been clashes in two locations and the results from those two booths have been delayed as a result.
Final results won't be available until Sept.14, Thaufeeq said.
Long lines of voters were reported at the 470 polling stations spread out over the Maldives' more than 200 islands.
Marie Harf, deputy spokeswoman for the U.S. State Department, issued a statement congratulating Maldivians on completing the first round of voting.
"The very high voter turnout showed the strong commitment of the people of Maldives to democratic government," she said.
"As the country prepares for a second round of voting on Sept. 28, we call on all parties to respect the democratic process and continue to allow for a free, fair and peaceful vote to take place."
Nasheed had said prior to the voting he was confident he would unseat Waheed in the second free election in the Maldives since 2008.
Nasheed, the country's first democratically elected president after three decades of autocratic rule, resigned last year amid protests from the opposition and security officials over the arrest of a senior judge.
Nasheed said at the time he was leaving office to avoid potential violence in the streets, but he later said he was forced out in a virtual coup by the army and national police, the BBC reported.
Waheed, who was Nasheed's vice president, has rejected the idea that his old boss was the victim of a coup.
The Maldives has a population of 450,000 and an economy based on tourism and fishing. Britain's The Guardian said it was attracting the interest of China and India, which have economic interests in the island.
Political observers are also interested in the election due to the nation's Muslim population.
"I've always said what happens in Maldives first, happens in the Middle East later," Nasheed told reporters this week.