what are the odds that we beat them 3 days in a row in their park? slim to zero.
I would be stunned if the Brewers didn't win the next 2 days to gain a split to predictably end the series.
The odds you beat them 3 in a row, having already beaten them 2 in a row, are excellent as compared to the odds before the series starts.
If you assume that the Brewers should win 60% of the games between the two teams, then the odds of the Nats winning tonight or any other single game in the series are 40%. Feel free to adjust the % to your liking, the math works in the same way regardless.
If you asked if the Nats could win 3 in a row before the start of the series, the odds would have been 40% to the 3rd power, or 6.4%. However, as already observed, the Nats no longer have to win 3 straight. They only have to win one.