Shvedova vs Errani (wimbledon)
All seriousness, Del Potro vs Federer(Olympics semi final). Neither player deserved to lose that match.
In womens, off top of my head i will say Azarenka vs Kerber at YEC, or Azarenka vs Serena at US Open.
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As for todays matches. I think Del Po vs Federer will go 3 no matter who wins. Del Po has been better recently, but Federer is federer, and Del Po's record against Federer is pretty poor.
So i'm going to say Federer in 3. 5-7,7-6,6-4
As for Sharapova vs Serena. I expect a closer match than the Olympics certainly. It's Depending on which Serena turns up tbh. If Serena the destroyer turns up, then it will be a beatdown. If not, i reckon it will be a tight match if Sharapova keeps up her good form.
Serena, 6-4,6-3 i'm going for.