As both sides reached a stalemate at Guandu and Cao Cao's forces ran out of supplies, Xun You advised Cao Cao, "Yuan Shao's supplies will be reaching in one day. Han Xun (韓𦳣), the officer leading the convoy, tends to underestimate the enemy. He can be easily defeated." Xun You also recommended Cao Cao's general Xu Huang to lead the attack on Han Xun. Cao Cao sent Xu Huang and Shi Huan () to raid Han Xun's convoy and they burnt the supplies. Later, Yuan Shao's adviser Xu You defected to Cao Cao's side and urged Cao to attack Yuan's supply depot at Wuchao (烏巢; southeast of present-day Yanjin County, Henan), which was guarded by Chunyu Qiong. While Cao Cao's other subordinates were suspicious about Xu You, only Xun You and Jia Xu advised Cao to heed Xu You's suggestion. Cao Cao then ordered Xun You and Cao Hong to remain behind to guard his main camp, while he personally led his forces to attack Wuchao and succeeded in destroying Yuan Shao's supplies and killed Chunyu Qiong in battle. As the tide turned against Yuan Shao, two of his generals, Zhang He and Gao Lan (), destroyed their own camps and led their men to defect and surrender to Cao Cao's side. When Zhang He and Gao Lan showed up at Cao Cao's main camp, Cao Hong felt suspicious and was reluctant to accept their surrender. Xun You told Cao Hong, "Zhang He was angry that Yuan Shao did not listen to him so he decided to defect. Sir, what's there to suspect about him?" Cao Hong then accepted their surrender.