John Lannan has been near his best during his last two spring training starts. (Paul Sancya/AP)

Monday morning, clarity replaced the uncertainty that hovered over John Lannan for weeks. Manager Davey Johnson declared Lannan would begin the season at the back of the Washington Nationals’ rotation. Not traded, as rumors had suggested. Not demoted to the minors, as his remaining option had made possible. The possibilities Lannan had pushed out of his mind — “just noise,” he said — vanished, at least for now.

With Chien-Ming Wang recovering from a strained left hamstring, Johnson made Lannan his fifth starter. He will not compete with Ross Detwiler, whom the Nationals have sent to the bullpen as a long reliever and emergency spot starter. Lannan, twice an opening day starter, has become a stalwart in the rotation, and he is not leaving it yet.

“John’s my guy,” Johnson said.

Lannan rewarded Johnson’s confidence Monday afternoon, retiring 12 of the first 13 batters he faced and holding the Houston Astros to two hits while striking out five in five innings. Lannan has been near his best during his past two spring training starts, keeping his sinker down in the zone, twirling breaking pitches for strikes.

“I kind of just gave myself a chance,” Lannan said. “I trusted it. I wasn’t so hard on myself. I just let it work.”

Since the Nationals signed Edwin Jackson in early February, Lannan had been on the outside looking in at a rotation he once headed. The Nationals had seven starting candidates, and Lannan was the only logical trade candidate. Suddenly, a left-hander with a 3.70 ERA in 2011, the second-longest tenured National behind Ryan Zimmerman, had his spot jeopardized.

General Manager Mike Rizzo said he had not shopped Lannan, but opposing teams called the Nationals with interest. As speculation grew, Lannan ignored it and focused on his craft. When his mind drifted and uncertainty crept in, Lannan shifted his thoughts to pitching.

“I know what I am,” said Lannan, who will make $5 million this year. “I’ve had success. That’s what I need to focus on, is what’s made me successful, and just get better. I haven’t really focused on anything that’s been outside.”

Lannan, 27, has gained four-plus years of major league experience, enough to understand and feel comfort in his muddled situation. Johnson never addressed Lannan’s situation with him, which is how Lannan wanted it.

“He doesn’t have to worry about me,” Lannan said. “He doesn’t have to worry. I want him to know he doesn’t need to come over here pat me on the back and say, ‘Hey, it’s going to be okay.’ I just don’t need that from him.”

Said Zimmerman: “John’s always done everything that they’ve asked him. But that’s part of the business. I don’t think he’s hurt or upset or anything by it. He understands that happens. Those things always have a way of working themselves out, like it did here.”

Lannan does not have the ceiling of Detwiler, the sixth overall pick in 2007, or the rocket arm of the other four Nationals’ starters. What he has is reliability. Lannan has pitched at least 180 innings with a sub-4.00 ERA three of the past four seasons. He consistently defies advanced metrics, chucking sinkers and producing groundballs.

“John does it every year,” Zimmerman said. “He throws 180, 200 innings and has a 3-something ERA. Which is pretty good. It’s fun playing behind him. He throws strikes. He gets infielders a lot of work. He doesn’t have any kind of sexy numbers or sexy stuff. He kind of just goes out there and gets it done.”

With Lannan solidly in the rotation, Detwiler will have to adjust to a new, unique role. During the spring, Detwiler has pitched once every four days, throwing two or three innings in each outing. The Nationals will be careful to keep him stretched out while still allowing him to pitch as needed.

“It’s just something I have to get used to,” Detwiler said. “So we’ll see. I think it’s just an adjustment I have to make. It’ll come. It’s not completely there, but it’ll come.

“I’m a big routine person. That’s what’s kind of throwing me off right now. I’m not on the same routine I’ve been on. That’s something I have to adjust to. I have to come up with a routine that gets me every fourth day, or that gets me ready whenever they call down there and say my name.”

Johnson expects Wang, who strained his hamstring March 15, to start the year on the disabled list and miss between four and six weeks, putting him on schedule to return by mid-to-late April. The Nationals will use caution, because re-injuring a hamstring strain can lead to severe complications. But they consider Wang ahead of schedule. Wang has been playing light catch and taking laps around the warning track, either briskly walking or slowly jogging.

“I’m amazed he’s doing what he’s doing already,” Johnson said.

Soon, then, the Nationals will have another decision to make with Lannan. They will have too many starters for not enough spots. The noise will rise again, and the Nationals can take comfort in knowing it will have no effect on John Lannan.

Nationals notes: First baseman Adam LaRoche , having spent all spring recovering from a bone bruise in his left foot, said he has no doubt he will be ready to play by opening day. But he is not keen on Johnson’s plans to platoon him with Mark DeRosa. “No comment,” LaRoche said. “That’s how I feel about that.” Johnson wants to protect LaRoche’s foot and his surgically repaired left shoulder. . . . Outfielder Roger Bernadina hit a two-run homer in the Nationals’ 7-4 win over the Astros, highlighting a two-game stretch in which he is 5 for 6 with a walk and two homers.