Yuan Shao's general Yan Liang crossed the Yellow River and besieged Cao Cao's fort at Boma.
Heeding his advisor Xun You's advice, Cao Cao led a battalion toward Yan Ford as a feint to trick Yuan Shao into believing that Cao Cao would attack his camp on the other side of the river.
Yuan Shao split off his troops from Liyang to counter Cao Cao's attack, leaving Yan Liang without any support at Boma.
Cao Cao then struck eastward to lift the siege on Boma.
In the ensuing battle, Yan Liang was killed by Guan Yu and Yuan Shao's army was routed.

Cao Cao decided to abandon the fort and evacuate its occupants to the south.
Taking advantage of the situation, Wen Chou and Liu Bei led 6,000 horsemen in pursuit.
Cao Cao anticipated the attack and prepared a distraction tactic.
He ordered his troops to discard their steeds, weapons and other valuables along the way.
Yuan Shao's forces broke their ranks to grab the valuables lying ahead.
Just as they were claiming the items, 600 of Cao Cao's elite cavalry that had been lying in ambush attacked them.
Yuan Shao's commander Wen Chou was killed and Liu Bei fled.
Having lost two of their generals in these relatively minor skirmishes prior to the primary conflict at Guandu resulted in a crushing blow to the morale of Yuan Shao's army.
Yuan Shao's general Yan Liang crossed the Yellow River and besieged Cao Cao's fort at Boma. Heeding his advisor Xun You's advice, Cao Cao led a battalion toward Yan Ford as a feint to trick Yuan Shao into believing that Cao Cao would attack his camp on the other side of the river. Yuan Shao split off his troops from Liyang to counter Cao Cao's attack, leaving Yan Liang without any support at Boma. Cao Cao then struck eastward to lift the siege on Boma. In the ensuing battle, Yan Liang was killed by Guan Yu and Yuan Shao's army was routed.
Cao Cao decided to abandon the fort and evacuate its occupants to the south. Taking advantage of the situation, Wen Chou and Liu Bei led 6,000 horsemen in pursuit. Cao Cao anticipated the attack and prepared a distraction tactic. He ordered his troops to discard their steeds, weapons and other valuables along the way. Yuan Shao's forces broke their ranks to grab the valuables lying ahead. Just as they were claiming the items, 600 of Cao Cao's elite cavalry that had been lying in ambush attacked them. Yuan Shao's commander Wen Chou was killed and Liu Bei fled. Having lost two of their generals in these relatively minor skirmishes prior to the primary conflict at Guandu resulted in a crushing blow to the morale of Yuan Shao's army.
Battle of Guandu