Odds For Fighting Game

I'm creating a fighting game where two opponents face off against each other in the ring. While I've been able to figure out the odds of a player winning based on previous wins/losses, I have yet to find a formula which modifies those odds based on opponent. For example:

Player 1: W:5 L:5 - 1/1 odds Player 2: W:5 L:0 - 1/5 odds

I want to calculate the odds that Player 1 will wins against player 2. Compounding this the players could be of different levels: if the players are within a few levels of each other, the odds should map closely to wins/losses. However, as the levels diverge, the odds of the lower level player winning reduce. As a swag:

Player 1 - W:5 L:5 - 1:1 odds

Against a level 8 - 1:2 Against a level 9 - 2:3 Against a level 10 - 1:1 Against a level 11 - 3:2 Against a level 12 - 2:1

These are just estimates, my sense is that there is a math formula out there which will calculate that - can anyone out there point me to what this could be?

Thanks...Chris

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