The only unexpected thing from the first day (IMO) was the pairs team for the US placing where they did, on top of that the Team Event led off with the 2 best disciplines for the US and the 2 worst disciplines for Russia.
Yep, Alexa and Brandon overperformed dramatically, beating the Japanese, Canadian, Italian, and Georgian pairs. Hubbell/Donohue also overperformed, they weren't expected to beat Nikita and Vika, but that is a fewer points differential than what was expected compared to what Alexa and Brandon did.
After the women's short, the US and Russia will most likely be tied, since the US lady (whoever it is) is most likely to finish third, behind the Russians and Japanese, thus erasing the two point lead the US currently have. She would be expected to finish third again in the free skate, a two point deficit. For the US to win gold, Alexa and Brandon will need to place third again in the free skate, and ideally, Sui/Han would beat M/G so that it's only a three point total deficit from the two weakest events for the US to try to make up in men's and dance.
In dance, the most likely scenario will be Chock/Bates placing second while Nikita and Vika place first, so then it's a four point deficit. If Vincent finishes first and Mark finishes last, then the two teams will be tied, and I have no clue how the tie breaker works, but that's quite unlikely to happen. More realistic is Vincent being 1st/2nd and Mark being 3rd/4th.
For the US to win team gold, Vincent will have to be first in the free skate, Alexa and Brandon need to be third in the free skate, the US ladies have to make sure they aren't beaten by any non-Russian or non-Japanese ladies. Then, Vikita need to make another mistake so that C/B finish ahead of them in dance. Even if all of those things go right, Mark will need to be fourth in the men's free for the US to win outright, or it goes to a tiebreaker if he's third.
And Hubbell/Donohue are not beating Vikita if Vikita don't make major mistakes, so there's no difference between subbing C/B or subbing H/D. Both American teams can beat the Russians if the Russians make major mistakes, and neither American team can beat the Russians if the Russians don't make major mistakes.