Tanner Roark is 12-7 this season and 19-8 since being called up in August 2013. He might also be the best trade Nats General Manager Mike Rizzo ever made. (Jonathan Newton/The Washington Post)

Tanner Roark stood in front of his clubhouse cubicle Friday night after his team’s fourth straight victory and his 12th win in his first full major league season. Not that he didn’t have his moments, but nothing overly remarkable in either his appearance or performance suggested he might just become the greatest trade Mike Rizzo ever made.

Postgame, in point of fact, Roark could have been any rotation guy in America.

His black hair was closely cropped, his full beard neatly groomed. Dressed in a designer orange T-shirt, jeans and sneakers, he stood a fairly sturdy but hardly imposing 6 foot 2.

Ninety minutes earlier the Washington Nationals right-hander had gone through an inning or two of trying to paint and forgetting to just pitch, starting to let the Pirates back in a game in which his offense spotted him five runs.

The most common word used to describe his uneven start by Manager Matt Williams, his teammates and Roark himself was “battled,” as in, “Tanner didn’t have his best stuff tonight, but he battled.”

Probably no one thought about it afterward in this even-keel, don’t-look-past-tomorrow clubhouse, yet “battled” is exactly the metaphor for Roark’s career, in which everything really has happened for a reason.

“You always have people that doubt you, who think you can’t do it,” Roark said before he left for the night. “The thing is, I’ve never had any doubt. It’s a boost of confidence to prove people wrong. I’ve been an underdog all my life. I still don’t mind it.”

Beyond Rizzo, the Nats general manager who swapped Roark and another prospect for a soon-to-be-done Cristian Guzman with the Texas Rangers in 2010, his immediate family and Roark himself, few people in baseball could have envisioned a struggling Class AAA starter in Syracuse two summers ago suddenly becoming a rock in the Nationals’ starting rotation — very possibly for years to come.

In 2012, he was 6-17 with an ERA of 4.39 in the International League. He unintentionally hit 11 batters. Control, command, you name it, Roark didn’t have it. It was his fifth year in pro baseball since the Rangers had taken him in the 25th round of the 2008 amateur draft, and the notion he would be tied for the most wins on a pennant-leading club in mid-August 2014 was a fantasy.

Roark is 12-7 this season and 19-8 since he was brought up last August. According to FanGraphs.com, another “Don’t-Hate, Calibrate” site suggested by Thomas Boswell, just two pitchers in baseball are ranked ahead of Roark when it comes to most improved pitchers in the all-important category of WAR (wins against replacement). (Until it served purpose in my column, of course, I thought WAR was an acronym for Wonks Against Real numbers.)

But this is all you have to know about Roark: 2012 wasn’t merely his career nadir. “Honestly, I think it was also my best year.”

“It was a tough year, no doubt,” he explained. “But even though numbers-wise it was my worst year, it actually became my best. Because mentally I overcame a lot.” For the first time in Roark’s career, he explained, “I learned not to worry about what happens to me on the field, to put whatever happened behind me and go after the next hitter.”

Roark has time and again illustrated his minor league education over the past year. On Friday, he tried to make a perfect pitch to Pirates center fielder Starling Marte in the fourth inning, a slider Marte socked over the left-center field wall for a two-run homer in a three-run Pittsburgh inning. But Roark didn’t melt down. He bore down, didn’t allow major damage to undo a strong start from his offense and got back to pitching rather than trying to be perfect.

As a veteran baseball sage remarked later, “I don’t know if [Stephen] Strasburg gets out of that inning without giving up six runs. Sometimes he gets so down on himself about what he did rather than what he’s doing.”

Afterward, Roark said he doesn’t beat himself up as much, adding, “I mean, you have to remember it is a kid’s sport. You hear that a lot. I’m still playing it as a kid.”

When I asked whether Strasburg and other young perfectionists need to have that attitude, Roark smartly didn’t bite, saying only, “Takes time.”

Rizzo said of Roark: “His blue-collar upbringing and his fierce competitiveness is what really attracted us to him as a trade candidate, and it has continued during his days as a big leaguer. He hasn’t changed a bit. Great teammate, nice smile, but tough as nails. Love the way he gets after it.”

At 27 years old, he is under team control in Washington through the 2019 season. The ways things are proceeding, Roark soon is going to have to find a new motivation than being the underdog.

“The biggest thing is the mental aspect of the game,” he said. “You’ve got talent, but now it becomes how you overcome certain situations. I got my opportunity. Now I’m running with it. First, my lifelong dream was to get to the big leagues. Now it’s to win a World Series. It’s next on my checklist.”

For more by Mike Wise, visit washingtonpost.com/wise.