Chris Archer will serve as the starting pitcher.
Cash said the Rays have a number of players who can hit second, but they opted for Morrison in the opener.
"There wasn't a specific reason why, other than we like him hitting at the top," Cash said. "We view him as a really good bat, and we want him to get as many at-bats as possible. ... We think he's going to be on base for us a lot."
The idea of batting Jennings in the middle of the order dates back to last spring.