Turkey's main opposition party retained its control over key cities and made huge gains elsewhere in Sunday's local elections, in a major upset to 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, or CHP, was leading by a wide margin in Turkey's largest city and economic hub, according to the state-run Anadolu Agency.