The ruling Justice and Development Party (AKP) candidate Ben Ali Yildirim on Sunday faced opposition Republican Peoples' Party (AKP) leader Akram Imam Oglu, who won an initial vote on March 31 before the election was annulled in the first such debate in Turkey since almost two decades.
In a poll of more than 30,000 residents on Monday morning, pollster Mack Danesmanlik found 46 percent of respondents said Imam Oglu was more successful than his rival, compared to 44 percent for Yildrim.
The company concluded that the Republican Peoples' Party candidate was likely to get the votes of 65 percent of those who did not vote in the March elections.
Mohammed Ali Kulat, the owner of the company, told Reuters "Imam Oglu talked more about what he would do, while Yildirim focused more on what he actually did."
Until Monday morning, Imam Oglu was 1.5 percentage points higher than his rival, according to latest polls.
In an interview with Reuters, Imam Oglu said the debate was a boost for him. "We are in a very good stage ... I am very clear in my opinion that after Sunday night, there was no drop in support at all, adding he expected a greater victory margin on Sunday.
The defeat of Erdogan's AKP in Istanbul, where he began his political career and served as mayor in the 1990s, would be a huge symbolic shock and a broader sign of declining support amid the economic downturn.