Karns promoted to fill in for Detwiler

WASHINGTON -- The Nationals placed Ross Detwiler on the 15-day disabled list on Sunday, leaving them in need of a starter for Tuesday's game against the Orioles. After Monday's game, Nationals manager Davey Johnson announced that Nathan Karns, the Nationals' 2012 Minor League Pitcher of the Year and No. 6 prospect, will fill that slot.

"It'll be a good test," Johnson said. "We'll find out [if he's ready]. … First time out in spring, he threw the ball good and then got a little anxious. But he's got a great arm. So he's going to start Tuesday."

Karns, 25, will be making his Major League debut. In nine starts with Double-A Harrisburg this season, he was 4-2 with a 4.60 ERA, including 55 strikeouts, 18 walks and one complete game. He was drafted by the Nationals out of Texas Tech in the 12th round of the 2009 First-Year Player Draft.

Left-hander Xavier Cedeno, who was called up for Monday's game but did not pitch, will return to Triple-A Syracuse to make room for Karns on the Nationals' roster.

Johnson said that Karns has a good fastball and hard breaking ball that's "more of a slurve." Nationals catcher Kurt Suzuki caught Karns in Spring Training and said that he liked what he saw.

"[We'll] try to keep him calm, he'll be a little amped up out there," Suzuki said. "It's his first start, he's going to be nervous. But the more fun he has, I think the better he will be."