“It was Strasburg’s day to throw,” Detwiler said . “I was kind of thinking a little bit. I remembered when he went down, Miggy [Batista] had to start. When they announced Miggy’s name, everybody booed. I was like, ‘Aw, man.’ Nobody really booed me, so that was good.”

Detwiler would have made Ms. Iowa proud in the Nationals’ 3-2 win over the Marlins. He breezed through five innings, allowing one run in three hits and a walk. He struck out five and pitched four 1-2-3 innings. He focused on peppering the strike zone, and he threw 50 of his 69 pitches for strikes.

The Nationals have made Detwiler a long reliever, a way to stash him on the roster because he has an option and they believe they have five pitchers better suited to start. Detwiler showed against a potent Marlins lineup, starting all of its regulars, that he can be as dominant as any Nationals starter.

Detwiler had made only one start all spring, in a minor league game. The Nationals had been throwing him one every four days, not every five, and he struggled to adjust. Tonight, he felt in his element.

“This is more the routine I’m used to,” Detwiler said. “It’s just kind of my realm. It’s what I’m used to. It made it a lot easier for me to get in my rhythm.”

The difference is time. When he starts, he knows he has a half-hour, and exactly a half-hour, to prepare. He can take his time, make sure he’s keeping the ball down, before going to the mound. In the bullpen, he has had a hard time rushing to warm up, not knowing how much time he’ll have.

Tonight, he felt just right. The Marlins brought their whole lineup. In the first, he struck out Giancarlo Stanton hacking at a high fastball. In the fifth he struck out Jose Reyes, one of the most whiff-resistant hitters in the majors. The key, he said, was throwing strikes early in the count.

“There’s a lot of guys in that lineup who can hurt you,” Detwiler said. “It really made me bear down, make sure I get ahead of people.”

Detwiler will not pitch again this spring. He will have a few more days to get used to his new schedule. If he can pitch out of the bullpen like he did tonight, he won’t have to worry about any boos.