Battle of Guandu
As another famous example of the weaker defeating the stronger in Chinese history, the Battle of Guandu took place in 200 AD in the Three Kingdoms period. It was a crucial victory for the leader Cao Cao in which he led a rebellion against Yuan Shao in Guandu region. This acted as a foundation for Cao Cao to unify the northern China.
In the late years of the Eastern Han Dynasty, Yuan Shao led an enormous trained army of 100 thousand soldiers in order to defeat Cao Cao, while the latter garrisoned Guandu, a good place for guard and confronted the enemy for months. Cao Cao sent troops to burn Yuan's food transport vehicles and led crack forces to raid Yuan army's grain station and burned up all provisions. The soldiers in Yuan's army with shattered morale either ran or surrendered. Cao Cao chased and attacked by all routes and wiped out over 70,000 enemies. Yuan Shao and his son fled to north with only 800 cavalries and never recovered ever since.