Sishui Gate

The Battle of Si Shui Gate (汜水関の戦い) was one of the first in a series of battles to topple the tyrant Dong Zhuo. In the novel and the games, Si Shui Gate and Hu Lao Gate are treated as two different locations. The games make it a likely adaption of the Battle of Dagu Gate, where Sun Jian defeated Dong Zhuo and Lu Bu in a more southern location.

Dynasty Warriors
After Dong Zhuo had seized power in the imperial court, he started a despotic reign which drew the ire of local warlords. Cao Cao initially allied himself with Dong Zhuo, but then tried to assassinate him which failed and Cao Cao was forced to flee. He soon gathered together others who were opposed to Dong Zhuo together in a coalition, and asked his childhood friend Yuan Shao to lead the fledgling Allied Forces.

The Allied Forces moved on Dong Zhuo's stronghold of Si Shui Gate which was defended by Li Jue and Hua Xiong. Initially, Sun Jian made a strong advance, and camped to rest his men, sending a request for supplies to Yuan Shu. Out of jealousy, Yuan Shu refused to send the supplies, causing Sun Jian to be defeated by an enemy counter attack. Meanwhile, Hua Xiong had defeated several officers of the allies in single combat, until Guan Yu volunteered to fight him. Guan Yu emerged victorious, and the allies were victorious. The aftermath left Guan Yu a well-known warrior with high respect.

Historical Information
Historically, it was Sun Jian who killed Hua Xiong. He also forced Lu Bu to retreat.