Morales moved through the Colorado Rockies' farm system as only a starter, and his first 13 appearances in the Majors were in that role.
When Morales pitches against the Cubs in place of the injured Josh Beckett, it will be his first start since 2009.
"I don't want to change anything. I'm going to try to compete," Morales said. "I'm going to try to do what I can do, I try to control what I can control, throw strikes and try to get the hitter out."
He has done that nicely out of the bullpen, going 0-2 with a 3.04 ERA in 22 appearances.
"Well, he's pitched multiple innings, and he's pitched ahead in the count with quality stuff," said Red Sox manager Bobby Valentine. "We'll see if he can't give us multiple innings again with pitching ahead in the count and quality stuff [as a starter]."
Morales hasn't had time to get stretched out for this start, but he did work 4 1/3 innings out of the bullpen on June 3 at Toronto.
"It depends on pitches per inning," Valentine said. "I think he can pitch more than five. Then we have the off-day with a stacked bullpen. Whatever he gives us should be fine."