This wasn't a regular season game. This was a must win PO game, so you have to go with your two best pitchers and that's what Cora did. And it worked out. You win with your best or you lose with your best. You don't go with your 3rd best.
I doubt Chappy will be available tomorrow, but Whitlock will be available for 2 innings tomorrow. Also, the rest of the Sox BP should be well rested.
Just need 5 good innings from Bello.