Washington left-hander John Lannan, who put his game back together again during a demotion to Class AA last summer, pitches against Florida during a spring training game earlier this month. (John McDonnell/The Washington Post)

Humbled and confused, back in a place he thought he’d left for good, John Lannan walked to the mound late last June wearing a Harrisburg Senators jersey. Less than three months after he had started on opening day for the second straight year, the Washington Nationals had sent him back to the minors. “It was a little weird when that national anthem started,” Lannan said. “There was no fireworks or anything.”

With this season’s opener two days away, Lannan’s six-week detour to the minors seems like only a blip. The Nationals gave Lannan a one-year, $2.75 million contract this offseason, the first in which he became eligible for arbitration. He will start the second game of the Nationals season, still a stalwart of their rotation. The doubt created by his miserable first three months of 2010 has vanished. Lannan emerged from his exile to Class AA not only repaired, but perhaps better than he had ever been before.

“At the time it hurt, but it was what I needed,” Lannan said. “It helped. It’s not like I went down there and it didn’t do anything for me. . . . I’ll never forget what happened. I’ll never forget getting sent down. I’ll never forget that feeling of being there. It’s a feeling that I don’t want to have ever again.”

When Lannan arrived at Nationals Park on June 21 last year, he wondered if he would still be a major leaguer. The day before, he had allowed 11 hits and five runs in four innings to the Chicago White Sox. His ERA sat at 5.76. Mentally, he had been taking the same approach as 2008 and 2009, when he accumulated a 3.89 ERA, ranking him right in front of Derek Lowe and Josh Beckett. But his ability to induce groundballs disappeared, replaced by a penchant for line drives.

“I just attacked guys, but my stuff wasn’t there,” Lannan said. “The ball was up, and I was just like, ‘Here, hit it.’ And they were hitting it, because my stuff wasn’t there.”

The Nationals chose Harrisburg because Randy Tomlin served as the Senators’ pitching coach. Tomlin had worked closely with Lannan in 2007, when he was the Class A Potomac pitching coach. Lannan started that season in Potomac, shot through the whole farm system and reached the majors by July. Tomlin wanted to restore what made that happen.

“The major point was to kind of remind him who he was,” Tomlin said. “He showed up the first day and said, ‘Whatever you say, we’ll do. I’m ready to go. Glad to be here. Let’s talk.’ ”

Talk was the first thing they did. Tomlin emphasized to Lannan that he had not built himself into a major league pitcher quickly, and he would not rebuild himself quickly.

Lannan threw a bullpen session as Tomlin watched. Tomlin noticed vast differences from 2007, insidious, gradual changes that Lannan did not realize had happened. Tomlin showed Lannan video from 2007 and from the bullpen session.

“I didn’t realize at the time, but I was throwing the ball pretty well” in 2007, Lannan said. “I didn’t realize it, because I just did it. I wasn’t thinking.”

He and Tomlin found that Lannan, during 2010, had started standing taller during his wind-up, having moved away from a crouched, athletic posture. The starting point prevented Lannan from hiding the ball in his wind-up. Lannan relies far more on deception and location than power, and without knowing it, he had virtually been telling batters what pitch was coming.

During 2010, Lannan had also emphasized to himself the importance of “getting on top of the ball” — making sure he threw in a way that created the sink he relies on for weak grounders. To Lannan, that meant raising his left arm higher. As he worked with Tomlin, he realized the higher arm slot actually decreased the sink. He could throw with his hand on top of the ball, from a slightly lower, more natural angle, and create the right amount of sink.

The final piece came in mid-July, during a bullpen session in Portland, Maine. “Hey, Randy,” he asked Tomlin before one pitch, “what do you think of this?” He had found the right arm angle, the right tempo — he felt right again.

“That felt really, really good,” Lannan said. “I had told myself that I wouldn’t tell them I was ready when I wasn’t ready. That wouldn’t be fair. I could have complained, ‘I shouldn’t belong here.’ But I knew that I should work on stuff down there, and when I was ready, I’d be ready. In Portland, I felt like I was ready.”

On Aug. 1, Lannan returned. He pitched five innings and allowed two runs against the Philadelphia Phillies, the team that knocked him out after 32 / 3 innings and five runs on opening day. Lannan made 11 more starts, compiling a 3.42 ERA and striking out 6.19 per nine innings, two more than his previous career rate.

In those last 11 starts, Lannan struck out 47 and walked 14, a 3.36 strikeout-to-walk ratio, the most crucial underlying factor of a pitcher’s success. For perspective, if Lannan reached a 3.36 strikeout-to-walk ratio during all of last season, he would have ranked eighth in the National League.

Lannan can be hard on himself, Tomlin said. When he went back to Harrisburg, Lannan learned to pitch like himself again, and to think less. “That’s what I’m trying to get to now,” Lannan said. “Just trust your natural ability. I went with it, and it got me to the big leagues.”