Guan Yu slays Yan Liang and Wen Chou

In Romance of the Three Kingdoms, during the Battle of Guandu, Yuan Shao's army is led by Wen Chou and Yan Liang. They attack Cao Cao's fortress at Baima. Some of Cao Cao's best warriors, such as Xu Huang, went to challenge Yan Liang, but were defeated. Eventually, Cao Cao reluctantly allowed Guan Yu to challenge Yan Liang. Guan Yu defeated Yan Liang without much effort. Wen Chou was out for revenge and challenged Cao Cao's army, but he too was easily defeated by Guan Yu.

What happened historically?

 * Historically, Yan Liang was indeed killed by Guan Yu, whether this was indeed as easy as described in Sanguo Yanyi is not known, but it seems unlikely.


 * Historically, Wen Chou was not slain by Guan Yu. Instead, he died at Yan Ford in battle with Cao Cao's troops.