Iit was far from certain that the 59-year-old Yameen, whose main political rivals were either jailed or in exile, would graciously accept defeat in Sunday's poll, observers said.
Official results showed Ibrahim Mohamed Solih, the compromise joint candidate of the weakened opposition, as the clear winner with 58.3 percent of the vote, the biggest margin of victory in any election since the advent of democracy in 2008.
Maldives election expected to cement president's grip on power
Nearly 90 percent of the 262,000 electorate turned out to vote, with some waiting in line for more than five hours as officials encountered technical glitches.
Celebrations broke out across the 1,200-island tropical archipelago popular with wealthy foreign tourists, with opposition supporters carrying yellow flags of Solih's Maldivian Democratic Party (MDP) and dancing in the streets.
However, events following the last election in 2013 suggest that the celebrations in the nation of 340,000 people may be premature.
In that election, former president Mohamed Nasheed won the most votes in the first round but the supreme court annuled the result and a subsequent second vote was postponed twice.
This gave Yameen, half-brother of the country's leader for 30 years until 2008, Maumoon Abdul Gayoom, enough time to forge alliances that helped him narrowly win a contested run-off.
The US State Department, which before the election warned it may take "appropriate measures" if the vote was not free and fair, on Monday called on Yameen to "respect the will of the people."
Regional superpower India, competing with China to retain its influence in the region, was the first to "heartily congratulate" Solih.
"This election marks not only the triumph of democratic forces in the Maldives, but also reflects the firm commitment to the values of democracy and the rule of law," the foreign ministry said.
"In keeping with our 'Neighbourhood First' Policy, India looks forward to working closely with the Maldives in further deepening our partnership."
China, which has loaned Yameen's government hundreds of millions of dollars for an infrastructure blitz, was yet to comment.
There were also no other candidates at Sunday's election held with all key dissidents either in jail or exile.
Earlier in the night Solih had called on Yameen to concede defeat once the tally showed he had an unassailable lead.
"I call on Yameen to respect the will of the people and bring about a peaceful, smooth transfer of power," he said on television.
He also urged the incumbent to immediately release scores of political prisoners, including former president Gayoom who was jailed along with the Chief Justice and another Supreme Court justice amid accusations there was a coup in the offing.
On the eve of the poll, police raided the campaign headquarters of the MDP and searched the building for several hours in a bid to stop what they called "illegal activities". There were no arrests.
Nasheed said the vote would "bring the country back to the democratic path", and said Yameen had no option but to concede defeat.
"He will not have people around him who will support him to fight on and stay," he told AFP.
Independent international monitors were barred from the election and only a handful of foreign media were allowed in to cover the poll.
The Asian Network for Free Elections, a foreign monitoring group that was denied access to the Maldives, said the campaign had been heavily tilted in favour of 59-year-old Yameen.
Police raid Maldives opposition HQ ahead of vote
The government has used "vaguely worded laws to silence dissent and to intimidate and imprison critics", some of whom have been assaulted and even murdered, according to Human Rights Watch.
On Monday the Maldivian government acknowledged that the main opposition candidate Solih had defeated President Yameen in the election.
"Candidate of the Maldivian Democratic Party... Honourable Solih, won the election, having received 134,616 votes," the foreign ministry said.
State media, which before the election gave very little coverage to the opposition, also showed Solih declaring himself the winner.
Yameen has yet to comment personally.
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