Most of the time, priors and posteriors match. If you expect the posterior to differ from your prior in a specific direction, then change your prior.

And thus, you should expect 99% of underdogs to lose and 99% of overdogs to win. If all you know is that a dog won, you should be 99% confident the dog was an overdog. If the standard narrative reports the underdog winning, that doesn't make the narrative impossible, but puts a burden of implausibility on it.