The siege of İnegöl took place between Agios Nikolaos, the governor of the fort, and the Kayı army under the command of Turgut Bey.

However, Osman eventually gave the command to Turgut Alp to go and besiege the neighboring fort of Yarhisar.

[2] Turgut Bey stormed the fort,[6] killing most of the garrison and executing Nikolaos (Osman conquered Yarhisar around the same time).

[7] This major conquest of a key fort in the Byzantine heartland of Anatolia led to the rise of the Kayi Beylik and to the establishment of the Ottoman Empire.

[2]The Byzantines were alarmed by Osman's rapid conquests and eventually fought him in a climactic battle at Bapheus.