Harrison, 27, will be the team's fifth different opening-day starter in the last five years, joining Kevin Millwood (2009), Scott Feldman (2010), C.J. Wilson (2011) and Colby Lewis (2012). He went 18-11 with a 3.29 ERA last season, which earned him a five-year, $55 million contract extension this winter.
Darvish, 26, went 16-9 with a 3.90 ERA last season, his first year in MLB after coming over from Japan. He went 4-0 with a 1.85 ERA in his final six starts of the season. The Rangers paid out more than $110 million between the posting fee and contract to acquire the right-hander last offseason.