Defending champion Beşiktaş slumped to a 3-2 away defeat against Medipol Başakşehir in the Turkish Süper Lig on Friday.
Italian forward Stefano Okaka grabbed a brace for Başakşehir, opening the scoring in the 40th minute and netting the home side's second in the 83rd minute.
Fredrik Gulbrandsen netted what proved to be the winner in the 85th minute.
Alex Teixeira and Michy Batshuayi were on the scoresheet for the Black Eagles.
The win puts Başakşehir in 14th spot on the table with nine points, while Beşiktaş remains at the third spot with 17 points.
