I still think it's Soderling beating Nadal at RG. All you need is the reaction of the tennnis world to tell you which is the bigger upset. Nadal losing to Rosol was talked about but the shock value was nowhere close to him losing to Soderling. I'm sure many Nadal fans would admit to crying when he lost at RG but I doubt any of them shed a tear at his loss to Rosol.
Rosol was much bigger upset than Soderling.
Rafa's loss to Soderling now
looks much bigger due to the fact he has won RG every year since he lost to Robin in 2009. However, let's rewind here. There is a reason Nadal was only an oddsmaker favorite of 1.07 vs Soderling. His form was visibly not as sharp, and he was playing a solid opponent.
If you go by the oddsmakers, and people who make a living trading tennis odds, Soderling beating Nadal wasn't even the biggest upset of the year, in fact, it wasn't even in the top 3.
No doubt, it was still a very big upset, and it is over-exemplified today due to Nadal not losing at RG since 2009. Yet, at the time the matches were played, Soderling was much more of a threat on Nadal's clay than Rosol was on grass. I remember that match vividly, and quite a few respectable tennis handicappers liked Soderling. No one knowledgable in the field of predicting tennis outcomes entertained the thought of Rosol winning, no one. The odds reflect that, as Rosol was a 55-1 underdog. Yet, at betfair you could lay 1-14 on Nadal to win vs Soderling.