Historicity
The Battle of Jiameng Pass was not documented in the historical text Records of the Three Kingdoms by Chen Shou. There is no mention of a duel between Ma Chao and Zhang Fei. Ma Chao's defection from Zhang Lu to Liu Bei's side is described in Ma's biography as follows:
Ma Chao could not get along well with Zhang Lu and they were suspicious of each other. When Ma Chao heard that Liu Bei was besieging Liu Zhang in Chengdu (Yi Province's capital), he secretly wrote a letter to Liu Bei, expressing his willingness to surrender. Liu Bei sent his men to receive Ma Chao, and Ma led his troops to outside Chengdu. This caused panic in the city and Liu Zhang surrendered. Liu Bei appointed Ma Chao as "General Who Pacifies the West" and placed him in charge of Linju (臨沮).
An annotation from Dianlue in Ma Chao's biography stated:
When Liu Bei heard that Ma Chao had arrived he was pleased and said, "Yi Province is mine." He then sent his men to meet Ma Chao and sent reinforcements and supplies to the latter. When Ma Chao reached Chengdu, he stationed his army north of the city and Chengdu fell (to Liu Bei) within 10 days of Ma Chao's arrival.
Nothing is mentioned about the roles Zhuge Liang, Yang Song and Li Hui played in Ma Chao's defection.
Read more about this topic: Battle Of Jiameng Pass