大败 and 大胜 are really lovable and hatable. They can be used with the same meaning but they are not always the same. Here are the tips for you to figure out how to differentiate 大败 and 大胜
When both are used as transitive verb, they have the same meaning:
defeat utterly; to put to rout. Examples:
Team A defeated utterly Team B.
She defeated her opponent in the first round in under half an hour.
When both are used as intransitive verb or noun, they have different meanings:
大败, intransitive verb: suffer a crushing defeat.
They suffered a crushing defeat in the battle.
大败, noun: a crushing defeat.
Their leader decided to investigate the reason for the crushing defeat.
大胜，noun: intransitive verb: win a big victory.
They won a great victory in the battle.
大胜，noun: a big victory.
We need a convincing victory.