I've noticed many players who have difficulty clearly articulating the first note of a piece. However, they clearly articulate the first note of later phrases. I think the reason for this is that the breath preceding these articulations originates from a different place. It is important to make sure that every breath you take starts with the mouthpiece placed securely on your chops, allowing you to breathe from the corners with your embouchure set for the first note that you play. Most players do this intuitively once they are a few bars into the piece, but I can't tell you how many players I've seen that seem to take the first breath with their chops separated from the mouthpiece. Try to make the first, second, and third (and so on) breath start exactly the same way. For those who don't currently do this, try it. I bet your batting average will go up significantly!