Turkish President Recep Tayyip Erdogan’s ruling AK Party has lost control of Istanbul after a re-run of the city’s mayoral election.

With nearly all ballots counted, main opposition party candidate Ekrem Imamoglu, 49, had a lead of 775,000 votes, a huge increase on the margin of 13,000 he achieved in the earlier election.

The March victory was annulled after the AKP alleged irregularities.

The result ends 25 years of AKP rule in Istanbul.

The AKP’s candidate, former PM Binali Yildirim, conceded to his opponent.

President Erdogan tweeted: “I congratulate Ekrem Imamoglu who has won the election based on preliminary results.”

The president 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, Ekrem Imamoglu, of the Republican People’s Party (CHP), said the result marked a “new beginning” for both Istanbul and Turkey. He said his supporters had “fixed democracy”.

“We are opening up a new page in Istanbul,” he added.

“On this new page, there will be justice, equality, love.”

Ekrem Imamoglu added that he was willing to work with President Erdogan, saying: “Mr. President, I am ready to work in harmony with you.”

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With 99% of votes counted, Ekrem Imamoglu had 54% of the vote and Binali Yildirim 45%.

Ekrem Imamoglu is the mayor of Istanbul’s Beylikduzu district but his name was barely known before he ran in the March election.

Binali Yildirim was a founding member of Recep Tayyip Erdogan’s AKP and was prime minister from 2016 until 2018, when Turkey became a presidential democracy and the role ceased to exist.

He was elected Speaker of the new parliament in February and before that served as minister of transportation and communication.

Ekrem Imamoglu’s victory of 13,000 votes in March was not enough for Binali Yildirim to accept defeat.

The AK Party alleged that votes were stolen and many ballot box observers did not have official approval, leading the election board to demand a re-run of the vote.

Critics argue that pressure from President Erdogan was behind the decision.

Istanbul is Turkey’s largest city, with a population of 15 million, not far short of a fifth of the country’s 80 million, and is also the nation’s business hub.

Local currency, the lira, down 10% this year, rose on news of the result.

Istanbul is also close to President Erdogan’s heart – his political career rose there as his AKP took power in the city a quarter of a century ago and he himself served as mayor from 1994 to 1998.

The city accounts for just short of a third of Turkey’s GDP. It has a $4 billion municipal budget which spawns lucrative contacts. The AKP has now lost control of it.

Part of Ekrem Imamoglu’s campaign was to allege the squandering of public money by the AKP.

Although less conservative as a whole than the AKP’s rural heartland, Istanbul still has conservative districts such as Fatih, but Ekrem Imamoglu also won there and in President Erdogan’s own childhood district of Beyoglu.

Turkey’s capital, Ankara, Istanbul and Izmir are all now in opposition hands.