(Paul Sancya/AP)

John Lannan existed for years as the most reliable member of the Nationals’ starting rotation, and tonight he will take the mound, in the consciousness of many fans, as the man who is not Stephen Strasburg.

The Nationals’ series finale tonight at Citi Field was to have been Strasburg’s final start, but they executed their planned shutdown five days early after Strasburg’s struggles Friday night against the Marlins. And so Lannan, the left-hander who twice started opening day, who has more wins in a Nationals uniform than all but one other pitcher, will make his return to the Nationals.

The Nationals take comfort in knowing exactly what they are going to get. Lannan throws his sinker low in the strike zone, induces gobs of groundballs and keeps them in  the game. His ceiling is not as high as the other members of the Nationals’ flame-throwing rotation, which is why the Nationals optioned him to Class AAA Syracuse out of spring training in favor of Ross Detwiler. But he is a viable, established major league pitcher.

Last year, Lannan posted a 3.70 ERA in 184 2/3 innings, and he led the Nationals with 10 wins. This year, the Nationals culled him from the minor leagues for two spot starts in doubleheaders. He pitched brilliantly in both starts, overcoming rocky first innings to win twice.

Lannan spent four seasons as a key figure in the organization as the Nationals lost and lost, and he had to watch from afar this season as they finally won big. Now he will get his chance to pitch in important games. He already had one chance this year, and he more than rose to the occasion.

On July 21, the Nationals lost the first game of a doubleheader to the Braves. They had lost the night before after blowing a nine-run lead. Their lead in the NL East had been whittled to 1 ½ games, the smallest it had been since early June. They had Lannan going on the mound in the second game.

In a desperate moment, Lannan delivered one of the defining performances of the Nationals’ season, a seven-inning gem in which he held the Braves scoreless for the final six innings. It stood as one of the biggest wins of the Nationals’ season. Lannan played many years for a loser, but he has won when it matters.

At Class AAA, Lannan made an adjustment to his delivery, standing taller on the mound in order to create a more acute downward angle. The work came to fruition in his final two starts, when he threw a pair of complete-game shutouts. Lannan dismissed those results as irrelevant to his work in the majors, saying it does not translate in the majors. And so tonight his season will start fresh, back where he belongs.

Strasburg will watch from the dugout, the most-discussed shagger of batting practice in the majors. The general reaction among teammates in the days since the Nationals’ decision came official has been empathy for Strasburg. A few have emphasized to Strasburg he did nothing to let them down, that they know the decision was out of his hands. Strasburg’s anger at the decision sprung from not only his competitiveness, but perhaps more from dread of disappointing his teammates. They want to let him know they are on his side.

Lannan may not be Strasburg, but tonight, in the start that would have been Strasburg’s, he will get the first chance to prove the Nationals lost an ace but regained a pitcher who is more than capable.

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