Xun Yu
When Lü Bu claimed his rule over Yan Province, many people gave up resistance and joined him; only Juancheng, Dong'e and Fan counties did not yield. At the time, Cheng Yu was guarding Juancheng with Cao Cao's chief strategist, Xun Yu, who analysed that the defences could only be successful if the officials guarding the three counties worked together. Xun Yu then asked Cheng Yu to oversee the defence of Dong'e County because he could probably convince his hometown to fight with him. Thus, Xun Yu stayed behind to watch over the fortress, and Cheng Yu went to Dong'e County. On his way, Cheng Yu passed by Fan County, where Si Yi (), an official under Lü Bu, was trying to persuade the prefect of Fan County to switch allegiance to his lord. Cheng Yu sought a meeting with the prefect and managed to persuade him to reject and kill Si Yi. When he arrived at Dong'e County, Xue Ti () and Zao Zhi () had already set up defences around the area, so Cheng Yu split his cavalry force out to take control of Cangting ford to block the advances of Lü Bu's strategist, Chen Gong. Xue Ti then formulated a strategy with Cheng Yu, which enabled the defences of the three counties until Cao Cao returned from Xu Province.