Turks headed to the polls Sunday for a historic runoff vote that President Recep Tayyip Erdogan entered as the firm favorite to extend two decades of his Islamic-rooted rule to 2028.

The NATO member's longest-serving leader defied critics and doubters by emerging with a comfortable lead against his secular challenger Kemal Kilicdaroglu in the first round on May 14.

Kilicdaroglu cobbled together a powerful coalition that included Erdogan's disenchanted former allies along with secular nationalists and religious conservatives.

Opposition supporters viewed it as a do-or-die chance to save Turkey from being turned into an autocracy by a leader whose consolidation of power rivals that of Ottoman sultans.

"I invite all my citizens to cast their ballot in order to get rid of this authoritarian regime and bring true freedom and democracy to this country," Kilicdaroglu said after casting his ballot in Turkey's first presidential runoff.

Erdogan's first-round lead came in the face of one of the world's worst cost-of-living crises, and with almost every opinion poll predicting his defeat.

The 69-year-old looked tired but at ease as he voted with his wife Emine in a conservative district of Istanbul.

"I ask my citizens to turn out and vote without complacency," Erdogan said.

Emir Bilgin heeded the Turkish leader's call.

"I'm going to vote for Erdogan. There's no one else like him," the 24-year-old said in a working-class Istanbul neighborhood where the future president grew up playing street football.