"I voted for Ahok because he has proven to be a leader who gets things done and he represents diversity", said Rudy Pardede after voting at a polling station in central Jakarta.
Basuki pointed to the "politicisation of religion" as a major factor behind the election result, which was not as close as polls had predicted.
Baswedan, an academic, has been accused of abandoning his moderate Islamic values during the campaign by cozying up to hardliners in a bid to win the support of Muslim voters angered by Purnama's alleged blasphemy.
Around seven million Indonesians are eligible to cast their vote in Jakarta's gubernatorial race as the second and the final round of election opened on Wednesday (19 April).
More than 7.2 million people were registered to vote in the polls, which are also important as politicians view them as a potential stepping stone to the presidency in 2019.
The head of the metropolitan police has ordered a ban on any mass gathering that could cause physical or psychological intimidation during the election, and says police will prevent the mass entry of people from outside the city.More news: Alleged leak reveals iPhone 8 plans
Religious tensions have been an undercurrent in the campaign, with Basukion trial for blasphemy over comments he made a year ago that many took to be insulting to Islam.
As deputy Jakarta governor in 2014, Ahok inherited the governorship from Joko Widodo who won the presidential election that year.
Baswedan, is backed by a conservative retired general, Prabowo Subianto, who lost to Widodo in a 2014 presidential vote. So called "quick count" results by research companies, which give a reliable indicator of voting, will be available within hours of the polls closing at 1 p.m.
Ahok is an ally of Indonesian President Joko Widodo, also known as Jokowi - in fact, he was his running mate during Widodo's own successful run for the governorship in 2012.
"We are all brothers and sisters. Whoever is elected, we must accept".
"The military and the police have guaranteed safety, so don't be afraid", he added on Metro TV, dressed in a plain white shirt rather than the trademark checkered shirt worn by his supporters.More news: David Fizdale Roasts Officials For 'Poorly Officiated' Game
A year ago the popular governor found himself embroiled in a blasphemy trial, after he cited a verse from the Koran, Al Maidah 51, telling voters they should not be deceived by religious leaders who claim Muslims can not vote for Christians.
Authorities in a neighbouring province on Java island searched private cars and public buses heading for Jakarta on Tuesday for sharp objects and explosives.
Baswedan, who is supported by the opposition Gerindra Party and Prosperous Justice Party, called on voters to forget the differences of the campaign, which has seen Purnama put on trial over blasphemy allegations.
After an anti-Purnama protest a year ago turned violent, authorities were taking no chances and over 60,000 security forces had been deployed.
That case is ongoing - on Thursday Ahok will hear prosecutors read their sentencing demands in court - and it has significantly dented his popularity.
Yesterday's election was held amid heightened security.More news: Easter: Nigerians should imbibe Christ's sacrificial spirit - Jonathan
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