For the years before this one, the Washington Nationals provided ample motivation to ignore them. And so some of the folks pining Wednesday night for Stephen Strasburg may not have recognized the tall left-hander standing on the Citi Field mound, black hair sprouting from under his cap. They may not have realized what John Lannan has done, the two opening day starts or the 200-inning season. They may have learned that the Nationals are not replacing their shelved ace with an empty uniform, but rather an accomplished major leaguer with a bat-deadening sinker and, after a year in the minors, something to prove.

Strasburg’s spot in the rotation came up for the first time since the Nationals shut him down for the season, and Lannan made the moment sting a little less. In the Nationals’ 2-0 victory over the New York Mets, Lannan fired 52 / 3 scoreless innings on five hits, all singles, and one walk. His fastball hovered in the low-90s, not near triple digits. His breaking ball kept batters honest rather than buckling their knees. Lannan still delivered results like an ace.

“Tonight, these guys were over there licking their chops,” shortstop Ian Desmond said. “They finally get to face a starter that’s not throwing 95 or 96. He comes and shuts them down. He did his job. I think that’s what we should expect from them the rest of the way.”

The Nationals’ 12th victory in 15 games pushed their lead in the National League East to a season-high 81 / 2 games over the Atlanta Braves and dropped their magic number on the Braves to 11. The Nationals have pushed the Braves to the brink, and they have a chance to knock them over it during a three-game series this weekend in Atlanta.

“You can definitely feel the difference,” Lannan said. “Being on this team right now is incredible. You can not only see it, but you can feel the chemistry and everything. It’s something special.”

The Nationals’ sweep of the Mets also served to remind how much more they are than Strasburg. They have the organizational depth to summon an established pitcher from Class AAA — for the year, including his two cameo starts in doubleheaders, Lannan is 3-0 with a 2.41 ERA with the Nationals. They still have Ryan Zimmerman, whose homer off Matt Harvey to lead off the fourth provided the night’s decisive run.

The Nationals have seized full control of the division under unprecedented circumstances. In the middle stands Lannan. He replaced a healthy, dominant pitcher the Nationals voluntarily removed from competition. He had spent almost the entire year at Class AAA even after punching up a 3.70 ERA last season.

“It’s definitely strange,” Lannan said. “There’s a lot of strange things going on. What’s going on with Stras, it hasn’t happened before.”

As Lannan spoke in the Nationals’ clubhouse, as if to hammer the point home, Strasburg walked behind him to fish something out of his locker. Despite the obvious story line, Lannan pushed aside the circumstances.

“He doesn’t get caught up in things,” Zimmerman said. “He goes out, he knows who he is. He knows what it takes for himself to be successful, and that’s what he does.”

Lannan was cognizant of how he differed from the other members of the Nationals. He thrives on groundballs and guile. They formed the hardest-throwing rotation on record.

“It’s been hard,” Lannan said. “I’m not going to say I went out there and tried to throw 96. But this rotation is different. Every five days, when Stephen was in it, it was just different. Day after day, just no giving up. I had to just not try to do what they do. I’m not necessarily that type of pitcher. But I do like to compete.”

Lannan, who grew up on Long Island, took the mound in front of at least 20 family members and friends. He stayed in total command, back where he believed he belonged. He stood tall on the mound, concealing the lower half of his face with his black glove.

Lannan had not pitched in 13 days, when he ended his minor league season with consecutive shutouts. He could not have been sharper. He induced 11 groundball outs compared to three flyouts, the exact ratio he wants, and mixed in two strikeouts. In his first five innings, Lannan allowed only one runner past first base.

Harvey struck out 10 Nationals in five-plus innings. The Nationals loaded the bases with no outs in the sixth inning, but still came away with nothing. Lannan never pitched with more than a 1-0 lead. With no margin for error, he kept the Nationals ahead. No matter how hard he throws, Strasburg could not have allowed negative runs.

“If you’re not pulling it for him, you’re not human,” reliever Sean Burnett said of Lannan. “To see what he went through in late March, and the way he handled it, he earned a lot of respect in this clubhouse.”

Lannan could have pitched deeper into the game had Manager Davey Johnson allowed it. Lannan’s walk of Lucas Duda in the sixth inning put runners on first and second with two outs. Lannan had thrown only 81 pitches, none of them hit exceedingly hard.

Johnson climbed the dugout steps and motioned for the bullpen. Because of Lannan’s long layoff, he did not want to tax him. Johnson summoned right-hander Christian Garcia to face Kelly Shoppach. Garcia’s first-pitch curveball drilled Shoppach in the shoulder, which loaded the bases. Ike Davis smashed a deep fly ball to center field, which Bryce Harper tracked down to end the inning.

Lannan watched from the dugout as the book on his start closed. Desmond’s 23rd homer gave the Nationals breathing room. The ninth inning became an adventure. Burnett made his first appearance after resting an irritated nerve in his left elbow for 10 days. He left with two outs and two on, before Drew Storen sealed the sweep by getting pinch-hitter Daniel Murphy to fly out to center.

The Nationals, of course, lost plenty by sending Strasburg to the bench. They may not have improved, but that does not mean they didn’t gain something by placing Lannan back in the rotation.

“I don’t think anybody in here was concerned with what John was going to give us,” Desmond said. “We’ve all see him enough. We didn’t really feel like he needed to prove anything to us.

“Pretty inspiring story, you know?”