Different year, different expectations. Last year Dennis was an unknown as to how he would play and really had nothing to lose. He shot great because of it and he fed off the emotion.
This year because of the success he had last year there was alot more expectation for him to have another great performance and such a thing has the ability to put a whole different mindset into the game and the same emotion that fueled him when riding a high last year put added pressure on him when now being expected to perform and it hurt his game.
There is a reason I think that robots like the Taiwanese are the best players in the world, they are far more immune to the above because they block out emotion when playing the game.
Emotion can sometimes help you out when things are going well but they can often be your worst enemy when the wheels fall off.