He looked considerably better as the tournament went on, a lot of people are quick to judge and say "its an excuse blah blah", but when you are actually in that position, they really play a factor. Familiarity, comfort level, climate, language, etc all of these factor in how we perform, and different people react to them in different ways. Some people adapt very quickly, while some not at all.
For example I was very good in math in high school, but when I entered the University it was a different culture, and the people I was dealing with are from the richer parts of the society. All of a sudden my school performance is taking a dip. It was only when I got comfortable with the environment that I was able to perform like I used to.