A man casts his ballot at a polling station in Istanbul, Turkey, June 23, 2019. (Xinhua/Xu Suhui)

ISTANBUL, June 23 (Xinhua) -- Ekrem Imamoglu, the candidate for the main opposition the Republican People's Party (CHP), is winning the Istanbul mayorship again on Sunday, this time with a wide margin.

Unofficial preliminary result, quoted by the state-run Anadolu Agency, showed Imamoglu garnering 54.03 percent of the votes, while his rival Binali Yildirim from the ruling Justice and Development Party (AKP) had 45.09 percent, as 99.37 percent of the ballots were counted.

In a televised speech, Yildirim admitted a clear victory for Imamoglu. "We will try to support him in every work he will do on behalf of Istanbulites," the former prime minister said.

Speaking live on TV, Imamoglu called on observers not to leave the ballot boxes until the result is finalized. "Under my rule, lavishness, arrogance, wasteful spending and polarization will end," he said.

Imamoglu, who was the mayor of Istanbul's Beylikduzu district for five years, beat Yildirim by a margin of some 13,000 votes in the first election on March 31, when the country held local elections, but the result was annulled by the Supreme Election Board over AKP's claims of irregularities.

Imamoglu served as Istanbul mayor for less than one month before he was disqualified by the election board on May 6 as it called for a re-election on June 23.

The election is seen as a turning point for the country's future, as it ends the AKP's 25-year-old hold on Istanbul, Turkey's economic hub that accounts for one third of the whole gross domestic product.

"If we lose Istanbul, we stumble in Turkey," Turkish President and AKP Chairman Recep Tayyip Erdogan once said.

The AKP lost major cities like Ankara, Izmir and Antalya in the March local elections.