The move allows the Rangers to "split up" their left-handers, with Derek Holland pitching on Wednesday. But manager Ron Washington said that was not the reason why the Rangers made the switch.
"We wanted to keep Darvish pitching on four days' rest," Washington said. "He pitched, what, once a week in Japan? We want him to get used to four days down and then pitching on the fifth day. It just so happens to split the left-handers."
The Rangers were able to use Monday's off-day to make the switch. Darvish will start Thursday, and his following start will be on Tuesday against the Yankees at the Ballpark in Arlington. The Rangers are also off April 26, and that would give Washington another chance to juggle his rotation.
If Darvish pitches on four days' rest again, he would pitch April 29 against the Rays at the Ballpark. If the Rangers stay in rotation, Darvish would pitch April 30 in Toronto.
"We haven't gotten that far yet," Washington said.
Harrison will be pitching on six days' rest when he takes the mound on Friday. His last start was in a 4-1 victory over the Twins last Friday, and that left him 2-0 with a 0.64 ERA in two starts.
"You want to get the ball every fifth day," Harrison said. "I didn't work out that way, but I'll take a couple of extra days of rest and I'll be ready to go on Friday."