Jonathan Newton/WP

Ross Detwiler still has lingering tightness in his strained oblique muscle and will miss his next start, Nationals Manager Davey Johnson said after Tuesday’s 9-3 win over the Baltimore Orioles. Rookie right-hander Nate Karns, called up to take his place for what at first seemed like just one start, will make another and pitch in Detwiler’s next turn Sunday in Atlanta.

“He earned another start,” Johnson said.

The Nationals want to be cautious with Detwiler, who was placed on the disabled list this week but retroactively to May 16. Head trainer Lee Kuntz recommended Detwiler rest more because he still felt discomfort when he threw.

The Nationals were weighing their options on Tuesday, considering sending the inexperienced Karns, 25, back down to Class AA Harrisburg after the start and calling up a reliever as Detwiler progressed positively. But Detwiler’s tightness remained and Karns’s demeanor and performance in his major league impressed the Nationals.

Karns allowed three hits on five hits over 4 1/3 innings against the talented Orioles lineup. “He should be proud of what he did,” Johnson said. “That’s a hot-hitting ball club.”

>>> Jayson Werth is scheduled to begin his rehab assignment for his strained hamstring on Wednesday at Class A Potomac. Johnson said it’s unclear when Werth could return given the perplexing injury.