National Daily learned that in virtually all the ballots counted, the opposition party candidate, Ekrem Imamoglu, leads with 775,000 votes, recording wider margin of 13,000 than he had in the previous election.
It was noted that the victory of Imamoglu in March was annulled after the AKP alleged irregularities.
The current result terminates the 25 years of AKP dominance in Istanbul.
The AKP’s candidate, former Prime Minister Binali Yildirim, conceded to his opponent.
On Twitter, President Erdogan wrote: “I congratulate Ekrem Imamoglu who has won the election based on preliminary results.”
Mr. Erdogan had previously said that “whoever wins Istanbul, wins Turkey”. He has ruled the country since 2003 both as prime minister and now president, becoming the most powerful leader since Mustafa Kemal Atatürk, the founder of the modern Turkish republic.
In his victory speech, Mr. Imamoglu, of the Republican People’s Party (CHP), said the result marked a “new beginning” for both the city and the country. He said his supporters had “fixed democracy”.
“We are opening up a new page in Istanbul,” he said. “On this new page, there will be justice, equality, love.”
He added that he was willing to work with Mr. Erdogan, saying: “Mr. President, I am ready to work in harmony with you.”
With 99% of votes counted, Mr. Imamoglu had 54% of the vote and Mr. Yildirim 45%