“It’s a tough decision, but I think it’s best for the whole ball club,” Johnson said.

Detwiler (3-3, 3.88 ERA) has allowed 16 earned runs over 20 1/3 innings over his past four starts, including a laborious, 4 1/3-inning outing Friday night in a 7-4 Nationals win. Wang made his season debut in relief of Detwiler, hitting 94 mph with his sinker in three strong innings.

In spring training, the Nationals planned for Wang to be their fifth starter. Before he strained his hamstring during a March 15 spring start, causing him to miss the season’s first seven weeks, they considered Wang among their top three starters. The Nationals will put into their rotation a pitcher who won 19 games twice before major shoulder surgery derailed his career in July 2009.

“It would be very hard for me to have a 19-game winner who’s come back from arm surgery and to have him in the bullpen,” Johnson said. “Here’s a guy who’s been in pennant fights. He knows what the pressure is all about. So it’s a good opportunity for him and for us to be in the role he’s accustomed to, and that’s starting. It doesn’t lessen the fact that I think Detwiler is a heck of a pitcher.”

Detwiler took the news hard, Johnson said, “and I want him to take it that way.” Detwiler had pitched well enough at the start of the season to make the Nationals think twice about giving Wang his spot. But after his recent struggles, the Nationals chose Wang, who cannot pitch out of the bullpen regularly because of his shoulder history.

“There’s still a lot higher ceiling there for” Detwiler, Johnson said. “By the same token, there’s 25 guys on this ballclub. … 25 guys are going to be in roles and stronger as a group.”