The NATO member's footprint in both Europe and the Middle East makes the election's outcome as critical for Washington and Brussels as it is for Damascus and Moscow.
But Erdogan's first decade of economic revival and warming relations with Europe was followed by a second one filled with social and political turmoil.
He responded to a failed 2016 coup attempt with sweeping purges that sent chills through Turkish society and made him an increasingly uncomfortable partner for the West.
The emergence of Kemal Kilicdaroglu and his six-party alliance - a group that forms the type of broad-based coalition that Erdogan excelled at forging throughout his career - gives foreign allies and Turkish voters a clear alternative.
Polls suggest the 74-year-old secular opposition leader is within touching distance of breaking the 50 per cent threshold needed to win in the first round.
A runoff on May 28 could give Erdogan time to regroup and reframe the debate.
But he would still be hounded by Türkiye's most dire economic crisis of his time in power and disquiet over his government's stuttering response to a February earthquake that claimed more than 50,000 lives.
"CAN'T SEE MY FUTURE"
Kivanc Dal, an 18-year-old first-time voter, said economic woes would push him to back Kilicdaroglu. "I can't see my future," the university student told AFP in Istanbul on the eve of the vote.
Erdogan "can build as many tanks and weapons as he wants, but I have no respect for that as long as there is no penny in my pocket".
But kindergarten teacher Deniz Aydemir said Erdogan would get her vote, citing Türkiye's social and economic development in recent decades and dismissing the idea that a six-party coalition could govern effectively.
"Yes, there are high prices ... but at least there is prosperity," the 46-year-old said on Saturday.
Erdogan's campaign became increasingly tailored to his core supporters as election day neared.
He branded the opposition a "pro-LGBT" lobby that took orders from outlawed Kurdish militants and was bankrolled by the West.
Erdogan's ministers and pro-government media referred darkly to a Western "political coup" plot.
The opposition began to worry that Erdogan was scheming up ways to hold on to power at any cost.
The tensions boiled over when Istanbul's opposition Mayor Ekrem Imamoglu - a sworn foe of Erdogan who could become Kilicdaroglu's vice president - was pelted with rocks and bottles while touring Türkiye's conservative heartland.
