Same problem as Changping; the victors had larger numbers, and it wasn't even a classical formation battle. If you want to talk about the bloodiest formation battles, I'd nominate Fei River, where Jin destroyed a vastly superior Former Qin army.
I wouldn't say that the former Qin army was superior. Though they numbered about 300,000, they were nothing more than territorial levies with barely any training and a complete lack of coordination. They faced a disciplined Jin army that numbered 80,000. Using bribes and trickery, the former Qin army lost cohesion and became demoralized, wholly disintegrating. The headlong retreat by the former Qin army was a massacre.
Battle of Boju (506 BC):
Commanding the Wu army of 30,000, Sunzi annihilated a Chu army of 200,000 commanded by Nan Wa. Using the Wu Prince Fugai, masquerading as King Helu of Wu, Sunzi lured the Chu army into an ambush. The defeat destroyed the Chu army and forced the King Zhao of Chu to seek refuge in the state of Sui. If it were not for the partying by the Wu army and the intervention by Qin (resulting from Shen Wuxu begging and crying for seven days and seven nights), Chu is likely to have been annihilated.
Battle of Weishui (204 BC):
At the head of 50,000 troops, Han Xin dealt the 200,000 Chu army commanded by Long Ju, a devastating defeat. While the Chu army crossed the river, Han Xin undammed it, resulting in the vast majority of the Chu army drowning. Long Ju and the remainder were cut off by the river and annihilated.
Battle of Vercellae (101 BC):
6 full legions and auxiliaries commanded by Gaius Marius annihilated a Germanic Cimbri army numbering 210,000 using the superior Roman cavalry commanded by Lucius Cornelius Sulla. Granted, the numbers involved also include women and children since the Cimbri were undergoing a mass-migration.
Battle of Alesia (52 BC):
The army that Julius Caesar commanded numbered about 50,000, composing of twelve understrength legions with some auxiliaries forces. His Gallic opponent consisted of two forces - besiegers and the besieged. The besieged within Alesia was led by Vercingetorix and numbered 80,000. The besiegers composed of an estimated 120,000-250,000 troops. Total numbers about 330,000 Gallic troops against Caesar's 50,000 legionaries and auxiliaries.