Guan Yu's presence alone caused Cao Ren and his army to flee

Cao Ren was won over to the side of those of action. He placed Man Chong in command of the defenses of Fancheng, while he went outside to beat off Guan Yu. When the two forces met, Guan Yu called to his side Guan Ping and Liao Hua, to whom he gave certain orders. These two advanced, settled their array, and Liao Hua then rode out and offered a challenge. Zhai Yuan accepted it. But soon after the combat began, Liao Hua made as if he was defeated and turned to leave the field. Zhai Yuan went after him. The Jingzhou troops retired seven miles or so.

Soon the Jingzhou soldiers came again and offered battle, when Xiahou Cun and Zhai Yuan both went out. The maneuver of the preceding day was repeated, and the Jingzhou army retreated another seven miles. But suddenly there was a detonation behind the army of Cao Cao, and the rolling of drums as for attack. Cao Ren hastily called upon his troops to return. They did so; but Guan Ping and Liao Hua then turned and followed on their heels so that the troops of Cao Cao were thrown into confusion.

Cao Ren by this time had seen that a trap had been laid and he had fallen therein, so he hastily marched with one army to Xiangyang. He got to within a short distance of the city when he saw before him a handsome banner waving in the wind, and out came Guan Yu with his green-dragon saber ready to slay. Cao Ren was powerless from fear, and, fighting being impossible, he turned off into a bye-road for Xiangyang (Romance of the Three Kingdoms, Ch 73).