(I assume here that you're talking about admission to PhD programs.)
I'm not in computer science, so I can't speak with authority. We have a number of users here who are in US computer science departments and maybe one of them can step in.
However, I would think that first-author publications would not be essential for admission to good PhD programs in the US. Keep in mind that in the US system, most students would enter a PhD program immediately after their undergraduate (bachelor's) degree, without doing a masters first. These students would not necessarily have any publications at all. The admission committee would expect somewhat more from a student with a masters, but I'd think any publications, first-author or not, would be a pretty good sign of your research ability and preparation to start a PhD.
Another thing to note is that recommendation letters are very important for admission to US PhD programs. If your advisor writes you a letter which speaks highly of the work you did, that should help your application a lot.