A battle of strategy
Chess was a game of strategy and probability, meant to be played by the sharpest of minds as with every move of the opponent, a thousand potential moves opened for the player however only one of them is the right move to be made.
Ozriel was extremely confident in his own skills and he did not expect that Rudra could beat him in a game of chess. Although chess was not a representation of one's actual combat strategizing skill , in itself chess was a mini combat strategy game so winning in chess did hold some merit to a great mastermind.
Rudra used to play chess as a way to sharpen his brain after his rebirth , and he would play against the highest level of human created AI and manage to play 100/100 games to a draw.
This was the reason why Rudra was confident in playing against Ozriel as he did not think a being got much smarter than artificial intelligence who could process all probabilities in a matter of seconds.