Nationals manager Davey Johnson announced the move prior to Wednesday's game against the Rays. The Nats lost the series opener, 5-4, as Wang struggled to establish command of his trademark sinker, walking three batters while striking out only one and allowing seven hits.
"Chien-Ming is very valuable to us, and I feel like in the five [outings], he hasn't gotten better with his mechanics," Johnson said.
"He's still not getting on top [of the ball], he's delivering it out [wide] with that flat movement instead of the sink. I was hoping he could work it out starting, but in conversations with [pitching coach Steve] McCatty, I think it's going to be best to see if he can't work it out with less stress on him."
Following the game, Wang said he wasn't worried about his spot in the rotation, though he did express concern over his command.
"Every time we had a bullpen session, [McCatty] was trying to tell me that I need to stay back on top of the ball and feel more on the ball," Wang said through an interpreter. "I think I did OK during the bullpen, but I just didn't feel that well when I got out there."
Detwiler began the season as the Nats' No. 5 starter, going 3-3 with a 3.88 ERA in nine starts. However, in his last two starts he lasted just five and 4 1/3 innings, respectively, while allowing a combined nine runs. Wang started the season on the disabled list because of a strained left hamstring and was initially slated to be a long reliever after being activated on May 22. But after a solid three-inning outing in a May 25 win over the Braves, Wang replaced Detwiler in the rotation.
"I like his stuff; I like the hard work he's put in to get to where he's at," Johnson said of Wang after Tuesday night's loss. "I think there's a lot there. We need to figure it out. It's getting late -- and we will."
In his six outings since moving to the bullpen, Detwiler is 1-0 with one hold and a 1.35 ERA in 13 1/3 innings.
"If you compared his performance [Tuesday] night with his last two [starts], it's a totally different pitcher," Johnson said. "He was dominating [Tuesday] night, very aggressive going after the hitters. His last two starts, it was kind of like pitching defensively, kind of not attacking the hitter. I think staying in the bullpen, if anything, helped him."
Detwiler will start Sunday against the Orioles, Wang's next slated outing.