Henry Onyekuru was on target as Galatasaray handed a 2-0 defeat to rivals Besiktas and they took control of the Turkish Super Lig title race.
Fatih Terim's men headed into Sunday’s big game with a poor record of a win in their past 15 attempts in Istanbul derbies.
With title rivals Istanbul Basaksehir having dropped points against Sivasspor in Friday's encounter, the win places the title race in Galatasaray's hands.
They got the opener through Onyekuru moments before the first-half break. Fernando wrapped up the vital victory for the defending champions in the 54th minute.