A win in parliamentary elections for a coalition of his conservative Islamist-rooted AK Party (AKP), the nationalist MHP and others, also offered Mr Erdogan a boost. He says a vote for him is a vote for “stability”.
But when earthquakes struck the country earlier this year, the incumbent president faced widespread criticism for a sluggish response.
His 74-year-old opponent, Mr Kilicdaroglu, is the candidate of a six-party opposition alliance, and leads the Republican People’s Party (CHP) created by Mustafa Kemal Ataturk, modern Turkey’s founder.
The election will decide who leads Turkey, a country of 85 million people, and how it is governed.
Its currency has plunged to one-tenth of its value against the dollar in a decade.
And the country’s foreign policy could also be shaped by the election. In recent years the NATO member state has irked the West by cultivating ties with Russia and Gulf states.
It’s estimated around eight million eligible voters did not have their say in the first round of the election. Both candidates will hope to win them over in the run-off.
Turkey hosts the most refugees of any nation on Earth, with some five million migrants, more than three million of whom are Syrian, according to Interior Ministry data.
Third-place presidential candidate, the hard-line nationalist Sinan Ogan, endorsed Mr Erdogan based on a principle of “non-stop struggle (against) terrorism”, referring to pro-Kurdish groups. He achieved 5.17% of the vote in the first round.
Another nationalist, Umit Ozdag, leader of the anti-immigrant Victory Party (ZP), announced a deal declaring ZP’s support for Mr Kilicdaroglu, after he said he would repatriate immigrants. The ZP won 2.2% of the votes in this month’s parliamentary election.
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Turkish election goes to run-off
Turkey’s Kurds, who amount to about a fifth of the population, could also be crucial in the run-off.
The pro-Kurdish Peoples’ Democratic Party (HDP) party endorsed Mr Kilicdaroglu in the first round.
The results of the run-off are expected this evening.