'It was not a single group or party, but the whole of Istanbul and Turkey that won this election, ' Imamoglu said in his victory speech as scenes of his ecstatic supporters broke out across the city of 15 million.
Sellers emphasize the President's indirect threat to the opposition candidate.
Erdogan has already played down the importance of the re-run, saying last week that the choice of mayor was "only a change in the shop window" since the AKP controls nearly two-thirds of the city´s districts.
The victor of Istanbul's mayoral election re-run, Ekrem Imamoglu, said Sunday that the victory marked a "new beginning" for Turkey and offered to work closely with President Recep Tayyip Erdogan.
Istanbul mayoral candidate of the main opposition Republican People's Party (CHP) Ekrem Imamoglu, right, casts his vote with wife Dilek Imamoglu and son Semih.
His relentlessly upbeat campaign paid off with an emphatic win on tonight, extending his margin of victory from just 13,000 votes in March to more than 775,000. Imamoglu increased his lead from a March mayoral election by hundreds of thousands of votes, which made any attempt by the governing party to refute his victory increasingly unlikely.
Critics accused Erdogan of refusing to give up control of Istanbul, Turkey's economic powerhouse and a crucial source of patronage for Islamic conservatives since he won the mayorship himself a quarter of a century ago.
Binali Yıldırım, the ruling Justice and Development Party's candidate (AKP), had about 45%, Anadolu said.
The AKP's candidate, Binali Yildirim, a mild-mannered Erdogan loyalist who oversaw several huge transport projects and served as prime minister, had already struck a conciliatory tone earlier on Sunday.
Imamoglu faced the juggernaut of Erdogan´s ruling AKP party, which has been in power in Turkey since 2002 and remains the most popular political force nationwide. He presided over years of strong economic growth.
Controversially, Turkey's election board cancelled the vote and ordered another vote take place.
Opposition supporter Banu Kirmizigul said he only voted in the repeat election, inspired by Imamoglu's campaign.
Erdoğan has ruled Turkey since 2003, first as prime minister and then as president, becoming the country's most dominant politician since its founder, Mustafa Kemal Atatürk, almost a century ago.
Addressing Erdogan in a speech, Imamoglu said, "I'm ready to work with you" to solve Istanbul's problems.
Analysts say the loss could set off a Cabinet reshuffle in Ankara and adjustments to foreign policy.
"Turkey should now return to its real agenda, the election process should close", MHP party leader Devlet Bahceli said. "Talking of an early election would be among the worst things that can be done to our country".
Turkey's economy is now in recession and the United States, its North Atlantic Treaty Organisation ally, has threatened sanctions if Mr Erdogan goes ahead with plans to install Russian missile defences.
The uncertainty over the fate of Istanbul and potential delays in broader economic reforms have kept financial markets on edge.
Turkey's economy is now in recession and the United States, its North Atlantic Treaty Organisation ally, has threatened sanctions if Erdogan goes ahead with plans to install Russian missile defenses.