Ross Detwiler does not have much to worry about these days. He arrived here for spring training two weeks early, armed for the first time with certainty about his place in the Washington Nationals’ rotation. Detwiler married his longtime girlfriend this winter, then cut short the Hawaii honeymoon to visit U.S. troops in a war zone, an experience that awed and humbled him. The last time he stepped on a mound, he seized a win-or-go-home playoff game by the throat. He is taking up golf, and is still new enough to the game that it doesn’t frustrate him.

His only concern may come when he walks off a bullpen mound and sees Manager Davey Johnson stalking toward him. “He doesn’t beat around the bush at all,” Detwiler said. Detwiler knows Johnson will tell him, in no vague terms, to throw more curveballs and change-ups.

Detwiler will use this spring to try to step forward, at 26, as one of the best left-handed starters in baseball. Overshadowed by the rest of the Nationals’ rotation, Detwiler spent the final two months last season as perhaps their best starter, a lefty who could hit 96 mph and, on some nights, take over a game with one pitch. He marked his performances with newfound body language, all smiles and shrugs.

“It just comes with being comfortable, really,” Detwiler said.

Comfort defines this spring for Detwiler. The hip surgery that once threatened to derail his career is barely a memory. His rebuilt mechanics come to him easily. Last year, he briefly toggled between the bullpen and the rotation. This spring, he knows he has already earned a spot by virtue of his finish in 2012.

After winning the NL East in 2012, the Washington Nationals are coming into the year with a cacophony of hype. But Thomas Boswell says focusing on this year’s potential is missing the point. (Brad Horn/The Washington Post)

From July 17 through Sept. 20 last year, Detwiler went 9-4 with a 2.76 ERA. After he finished the regular season with two subpar outings, he helped extend the Nationals’ season in the National League Division Series, holding the St. Louis Cardinals to one unearned run in six innings.

“He’s just so kind of — not goofy, but he’s so relaxed,” catcher Kurt Suzuki said. “He has a good time. You see him smiling a lot.”

Detwiler accomplished the successful run by leaning on his sinking fastball. Last year, he threw fastballs on 80.3 percent of the pitches, more often than any other starter in the National League. One start, he shut out the Philadelphia Phillies for seven innings while throwing 85 sinkers in 88 pitches.

“He has an idea what he wants to do,” pitching coach Steve McCatty said. “Sometimes, he can be stubborn. But he’s learned how to change what his game plan is, because he’s seeing what’s going on, reading the situation of the games.”

The Nationals, especially Johnson, want Detwiler to throw more curves and change-ups, to keep hitters guessing and to set them up for later in the game. “I don’t think it’s about developing. I think it’s about trust,” Suzuki said. “He’s got it. It’s there. You have to be confident when you’re throwing it. I think towards the end of the year, he’s got more success with it, which allows him to be more confident. If he mixes some off-speed pitches in, I think it’ll put him over the top.”

As much as Detwiler thrived late last year, he relished a part of his offseason more. In December, the military asked Detwiler to join a holiday USO tour with reliever Craig Stammen, Capitals player Matt Hendricks and other celebrities. In order to make the trip, he left his honeymoon two days early.

Detwiler and the rest of the crew traveled on Air Force 2, making the first stop in Bahrain. Gen. Martin Dempsey gave a speech, and Detwiler knew he had made the right decision. “Every time that guy speaks,” Detwiler said, “you want step on a battlefield and protect something.”

Detwiler spent time on a destroyer in the Persian Gulf, 50 miles off the coast of Iran. He got to ride on an aircraft carrier and watch fighter planes taking off, accelerating from zero to 180 mph in three seconds. He flew on a Black Hawk helicopter in Kyrgyzstan; the pilot was a Nationals fan. He visited five bases in Afghanistan, including one that represented, Detwiler said, “the closest to Taliban headquarters you could possibly get.”

The scheduled portions of the seven days of the trip all lasted 15 or 16 hours, but Detwiler relished them all. He and Stammen spoke to crowds of troops at each stop, which he found awkward at first. As the trip continued, Detwiler felt more at ease.

At one show, Dempsey said he used to be a Yankees fan, but was converting to the Nationals. Some of the soldiers in the crowd booed at the mention of “Yankees.”

When Detwiler grabbed the microphone, he asked the crowd, “Did I hear some Red Sox fans out there?” After a few cheers, he paused and said, “Well, we went into Boston and swept the Red Sox last year.”

At forward operating bases, Detwiler milled around during lunch, sitting down and chatting with soldiers. He met a soldier from Joplin, Mo., who went to college with his wife. He ran into a guy in Kyrgyzstan he played summer baseball with in high school, whose mother taught him English.

“It’s crazy how close to home that kind of hits,” Detwiler said. “It was 19- to 22-year-old guys. You don’t really know what to say when they’re going to a battlefield. Do you try to pump him up, like he’s one of your teammates?”

One soldier told Detwiler how much it meant for him to come. “No,” Detwiler replied. “You don’t know how much it means to me to be here.”

“That’s the biggest thing I can possibly do, to give back to them,” Detwiler said. “I was able to go on my honeymoon because of them. I was able to choose my wife because of them.”

After the week ended, Detwiler returned home to his bride. He felt lucky to have gone, and he knew he never would have had the chance if he didn’t play baseball in Washington. He came home with one more reason to feel comfortable.