Ask the host for the inside scoop on her.
The clear advantage of meeting a woman at a party rather than out on the town is that she's not quite a stranger. Instead of making a potentially embarrassing advance when you start pulling the aforementioned subtle moves, check with the host for the scoop on the girl you're gunning for. Preferably, when the game is on a commercial break.
Did she come with someone? Is she taken, on the rebound, or on the market? Once you have the necessary information, let it inform what steps you take next. And again, don't feel the need to seal the deal. Just be the cool, charming dude you are and it just might happen that she asks about you. Yes, it can be that easy.