Casas went 0-for-2 with a walk and two RBI in Thursday's 10-9 loss to Baltimore.
Casas had a pair of productive outs -- a groundout and sacrifice fly -- while batting sixth for Boston. The 23-year-old is expected to be the team's primary first baseman, meaning he'll start against both lefties and righties, but he could slip further down the order against southpaws.