Personally I would start the game off with Williams for probably 2 innings and then go to Matthys in the 3rd. The positive of going with Matthys early is you can max out his innings if he has a great day. If he throws a 8 pitch inning than you can probably extend him to 4 innings instead of just the expected 3.
With the announcement of Matthys I think it will go like this.
Matthys for 4
Esquivel for 2
Williams for 2 and
Witt for 1
Witt is the guy with the most saves after Matthys but this is a really weird situation because Witt hasn't pitched in a long time. I know he didn't pitch during the Big 12 tournament or Regional. Flattery is the other guy I am expecting might see action.