Re: If you could change the outcome of one match in 2012
Olympic mixed Doubles final
For singles, I'd say Stosur vs Robson at USO.
For a non-Robson match, Serena vs Azarenka: USO. Partially because the reactions of Serena fans would have been fun to watch. But mostly because I cannot wait for the day when someone's able to step up to Serena and beat her when she's on form and allow for the question that Serena isn't the best player on tour any more. Dominance is boring.