OK, this happened to me last night... WHY???

In Game 2 of my series, my starter, Michael Fulmer pitched 7.2 innings (and got the win.)
In Game 3 of my series, after 9 we were tied, and all of my relievers had been used. Fulmer was inserted and pitched FIVE innings and got the loss.

Why would it have chosen a guy who pitched the game before (for almost 8 innings) as opposed to one of my starters that had 1-2 or 3 days rest?

Confused.

I'm guessing because your future starters had defined roles by HAL to start in those upcoming games, so he used someone without a more pending role, probably in a fatigued state.