Carlos Osorio/AP

Ross Ohlendorf has pitched well enough to remain in the Nationals’ rotation, but Manager Davey Johnson is concerned he may not be able to pitch long enough. After Ohlendorf allowed one run over five-plus innings and lowered his ERA to 2.49 in a 2-1 win over the Marlins, Johnson may still replace him with Tanner Roark five days from.

“That’s probably where we’re going to do,” Johnson said. “But I’ll make that decision probably tomorrow.”

The Nationals are 4-0 in Ohlendorf’s starts. In 12 total appearances, Ohlendorf has 34 strikeouts and 12 walks in 43 1/3 innings. He was caught off guard by Johnson’s plan to move him back to relief.

“I don’t know,” Ohlendorf said. “That’s the first I’ve heard of it. I’ve been enjoying starting. I’ll do whatever they ask.”

Ohlendorf came off the disabled list last week after he missed 17 games with shoulder inflammation. Ohlendorf went on the DL after an odd game in Detroit, when he came out of the bullpen and failed to throw with his usual velocity.

Ohlendorf cruised through five scoreless in 74 pitches. But Johnson noticed Ohlendorf tiring and ordered Roark to warm up. Johnson’s concerns proved prophetic. Ohlendorf threw four fastballs 85 miles per hour or slower to Christian Yelich, who blasted a homer to right field.

Ohlendorf insisted he had not worn down. The pitches to Yelich were purposeful “batting practice fastballs,” Ohlendorf said – he wanted to change speeds to keep Yelich off balance. Johnson had a different view.

“He just kind of ran out of gas, like he did before,” Johnson said. “But you never know with him because he puts a lot on it. Other times, it’s like he’s changing up off his fastball. But when he takes 10 miles off, he gets to scaring me a little bit.”

Since the Nationals called up Roark three weeks ago, he has been a versatile weapon out of the bullpen. He has gone 4-0 while allowed two earned runs in 17 innings. The Nationals would lose Roark’s durability out of the bullpen, but then rosters will expand Sept. 1 and the Nationals will have extra arms at their disposal, anyway.

“It’s definitely exciting,” Roark said. “I’ve been mostly a starter this whole season down in Triple-A but it’d definitely be different here up in the big leagues. I’d do my best, go out there and have fun and try to keep winning.”

In other Nationals’ rotation news, Ross Detwiler continues to make progress as he returns from a back strain that has kept him on the disabled list since July 4. Detwiler made 50 throws Tuesday afternoon from between 60 and 90 feet. He has yet to pitch off a mound, but he has been playing catch for the past five days.

“It’s coming out pretty good,” Detwiler said. “It feels better than I have all year. We’re on the right path.”

Manager Davey Johnson doubts Detwiler will be able to return by the end of this season. Detwiler wants to, though. When asked when he might pitch off a mound again, Detwiler replied, “Not soon enough.”

Time may be too tight. The Nationals would want Detwiler to go through an arm strengthening program akin to spring training. They have placed him on the 60-day DL, and it will be another two weeks before Detwiler has spent 60 days on the shelf.

Head athletic trainer Lee Kuntz “kind of sat me down and got rid of all those thoughts,” Detwiler said. “I want to go a whole lot quicker than I am.  The severity of the injury, they want to take it slow and make sure we get everything right by the end. Luckily, there’s still a window for me to get out there.”