Which battle established the political supremacy of the British rule in India?

In the standard answer keys of several competitive state civil service exams, including the West Bengal Civil Services (WBCS), the Battle of Plassey (1757) is recognized as the definitive event that established the initial political supremacy and laid the concrete foundation of British rule in India. While the Battle of Buxar (1764) firmly consolidated and legalized this authority through the Diwani rights, the initial political breakthrough and supremacy dates back to Clive's victory at Plassey.