K8a

And suddenly the US Open Mens Winner is wide open

Tsvetana Pironkova to beat Alize Cornet at 2.01 with Pinnacle
I'll continue with this for obvious reasons. Like @matrixman, I'd have liked the price on her to beat Keys more, but this is also good at above evens. I think that Pironkova is actually a slight favorite here, as Cornet didn't impress in any of her matches so far, perhaps apart from the Keys meeting. She can also go mad at times, while Pironkova seems to be almost zen at the moment ?.

Shelby Rogers vs Petra Kvitova, Total number of sets - 3 @2.62 with bet365 
I like Rogers' chances of winning at least one set here. On the other hand it's hard to imagine Kvitova losing in straight sets. Therefore I'm choosing to go with both players winning a set on this one.