Not even close.. Soderling defeating Rafa at the French was a much bigger upset, and even then, I wouldn't consider that the biggest upset in men's tennis, although it is certainly up there. Rosol beating Rafa was not entirely surprising, at least for, even soon after the match. Yes, it was still rather unbelievable that Rosol pulled it off, however, remember that Rafa was down so many times at Wimbledon throughout the years and he has narrowly escape each time, a couple times due to some luck on his side. Kendrick was 2 points away from winning their match in 2006, Soderling had a break? or had break points in the 5th set in 2007, Youzhny was up 2 sets to love in 2007, Federer had his chances in the 5th set in 2008, and Petzschner/Haase also had their chances to win their matches against Rafa in 2010. So I'm not sure how a player, as in Rosol, who was able to take that one extra step all those players before him couldn't is considered a huge upset.
Chang beating Lendl at the French Open is arguably one of the biggest upsets. Chang obviously very young, far less experienced and Lendl was a multi slam winner both overall and at Roland Garros.
nadal has never been very dominant in the first week of wimbledon. he scaped many times due to his fighting spirit, antics and also choking opponents.
nadal in RG on the other hand has always been dominant all the way. plus, you also have to consider the h2h before the match. while soderling had curiosuly pushed nadal to 5 in the first week of wimbledon before, he had been crushed by nadal only a few weeks ago in rome. nobody ever thought soderling could beat nadal whereas with a player like rosol, strong serve, big game, etc in the first week of wimbledon with the possibility of a closed roof, you could figure he had a chance, albeit a really small one.
soderling was beneffited by the environment in that RG match, though. humid wheather made conditions slower and lowered the power of nadal's topsin and that somehow allowed a fast court player like soda to play at his very best. a couple of years later he'd beat federer in the same court under virtually the same wheather conditions.
both were huge upsets but soda's probly the biggest one in the history of the open era.