I'm at the rats as well, and like you, not using an emulator. I know on at least one play through a few years back I got through with only one fight, but it is somewhat random. And of course now that I need to get through with one fight I can't seem to do it. To help yourself out though, let the timer run out once. After that you'll be outside the opera and you can save. After it runs out once you don't have to go through the entire opera scene again. Also, if you can't seem to get past the first rat, leave the room and go back. His position will reset which is especially helpful if he wanders far away. Aside from that though it'll likely take a lot of luck and resets. You may have to suck it up and gain some experience though. Anywhere from 1-3 battles wouldn't normally lead to a level gain there if I'm not mistaken. If you can get by with 3 or less I say take it.