Preparation.
Clayton Kershaw not only warms up then studies the lineup for an upcoming game, but he also takes a moment to sit in the dugout, look out onto the field and mentally prepare for the job to come. In the photo above, via a tweet by the @Dodgers, he is shown taking some time before the game to get his mind in the right place. He's the best there is, and his physical and mental routine are the foundation for his excellence.
Last nights performance is an example of the outcome we've come to expect from Kershaw.