I'm sure a lot of you figured this out by now but I just realized it so maybe it'll help others.
The CPU doesn't choose the starting pitcher out of random. It matches up with # starter you choose. For example, you pick your #3 starter for the game, the CPU will take the #3 or 3rd Best SP on the roster and face you. You pick your #5, the CPU will choose it's 5th best SP.
Just want to share that so it may help you in matchups.