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Once Gio Gonzalez finished his seven two-run innings Tuesday night in St. Louis, he assumed he had finished his season. He had no problem with the Nationals’ rotation staying on turn and letting Tanner Roark pitch Sunday, the final day of the season. “I was packed up, ready to go,” Gonzalez said.

And then Manager Davey Johnson approached him. Johnson, as he explained yesterday, wants to finish his managerial career at least 300 games above .500. If the Nationals lose tonight, they would have to win tomorrow to ensure Johnson finishes his career with 1,372-1,071 record. Johnson wanted Gonzalez to start to give him the best chance to win, and Gonzalez, after initial hesitation, accepted.

“I talked to Davey a little bit about it,” Gonzalez said. “I think it would be nice to let my body recover, try to get ready for next year mentally. It’s nice when you have the skip come up to you and say it would be truly an honor for you to go up there and pitch, not only for yourself but for me, too. You take that to heart, and you understand it. I’ll be the last starting pitcher for him. It’s something that I’ll always remember.”

Gonzalez’s start will also allow him to shoot for two benchmarks. With eight strikeouts and 4 2/3 innings, Gonzalez can reach 200 in both categories.

“They’re great,” Gonzalez said. “It’s always nice to have. At the same time, I think the biggest focus is pitching the last game of Davey’s career. That to me is truly an honor. To me, that’s a milestone. To get to pitch for not only a legend in baseball, a man who helped manage to get [Washington] to the playoffs for the first time in [79] years, all that speaks for itself. Davey has helped in so many ways. You want to make sure you give him a nice exit.”

While Gonzalez will start, first baseman Adam LaRoche is done for the season with a slight biceps strain. Chad Tracy will start at first base tonight in his place.

After LaRoche finished sixth in the MVP vote last year, this season has been a letdown. LaRoche hit .237/.332/.403. His .735 OPS marks the lowest of his career aside from the injury-plagued, surgery-shortened 2011 season with the Nationals LaRoche, 33, is under contract for $12 million next season.