Castillo threw a sim game Sunday, Kevin Acee of The San Diego Union-Tribune reports.
Castillo has been brought along slowly this spring after an injury-plagued 2019 campaign in which he was limited to 8.2 combined major- and minor-league innings. With a simulated game now in the books, Castillo could feasibly earn a spot on the Opening Day roster if he's able to pitch in a few Cactus League games before the end of spring training.