Turkey’s main opposition party retained its control over key cities and made huge gains elsewhere in local elections on Sunday. The results are a major upset for President Recep Tayyip Erdogan, who had set his sights on retaking control of those urban areas. With more than 90% of ballot boxes counted, incumbent Istanbul Mayor Ekrem Imamoglu, of the Republican People’s Party (CHP) led by a wide margin in Turkey’s largest city and economic hub, according to the state-run Anadolu Agency. Mansur Yavas, mayor of the capital, Ankara, retained his seat with a stunning 25-point difference over his cha…