India took unassailable lead when it won the second match of the three match series. Here unassailable is the word used in the sentence.

no one could ever believe the dentist was arrested because his reputation was unassailable

Brenda's claim that she was exempt from taxation because she had earned no money was unassailable.

invincible, impregnable and incontestable.

Adjective: Not open to attack or assault, as by military force, brute strength, or logical argument; not subject to denial or dispute.

Example: Shakespeare's genius gives his works an unassailable position in world literature.

"No one is more dangerous than he who imagines himself pure in heart: for his purity, by definition, is unassailable." -- James Baldwin