I can assure you it is much tougher to beat a player who has aleady won a grandslam in a grandslam final as opposed to a grandslam semi final.
A) They are more experienced, been there and done it and can control their emotions a lot better.
B) Its harder to play well under the most severest of pressure.
C) It is EXACTLY TRUE!
A true fan is one that indulges himself within the game - not the player's that play the game.