Ryan Zimmerman belts his 18th home run of the season in the first inning, and then adds his 19th two innings later to give starter Tanner Roark all the offense he would need. (Marc Serota/Getty Images)

At the trade deadline in 2010, Tanner Roark amounted to what baseball people call “inventory” — a spare arm to suck up innings in the bushes. It only took a journeyman infielder for the Washington Nationals to pry him and another Class AA pitcher from the Texas Rangers. Roark refused to the let the label stick. He climbed up the Nationals’ farm system. He earned an invitation to major league spring training. He joined the Nationals’ bullpen, and in long relief he pitched like a sorcerer.

What the Nationals have now in Roark they aren’t exactly sure, but in the final month of a lost season they intend to find out. Saturday night, Roark led the Nationals to a 9-2 victory with six scoreless innings in the first start of his major league career, a masterful four-hit, buzz-sawing of the Miami Marlins. With Bryce Harper scratched 10 minutes before first pitch, Ryan Zimmerman’s two home runs and a spectacular play at third base led the Nationals’ support of Roark.

Friday afternoon, Roark said he would take a simple plan into his first start: “Don’t try to change anything.” With red socks pulled high and black hair flowing out the back of his cap, Roark marched to and from the mound with a stoic, unchanging expression. The 26-year-old right-hander attacked with a low-90s fastball and a barrage of strikes. He retired the first nine hitters he faced, walked none, struck out four and chucked only 71 pitches. His outing suggested he had done this before, even though he had not.

“Yeah, I’m a little surprised,” Roark said. “But I don’t want to change anything. I just want to be the same old person I’ve always been and keep going right at guys.”

Saturday morning, Baseball Prospectus pegged the Nationals’ postseason odds at 0.6 percent, and they grew dimmer when the Cincinnati Reds won again in the afternoon. With 21 games left, the Nationals still trail the Reds by eight games for the second wild-card spot. Manager Davey Johnson insisted he had not shifted focus away from a miracle playoff run. But the Nationals, really, can start trying to answer questions for next year.

“I knew I had something” in Roark, Johnson said. “He’ll make his next start. I’m not that stupid.”

Roark, trying to shove his way into consideration for a rotation spot, may be one revelation. After his six scoreless innings Saturday, Roark owns a 0.94 ERA 28 2 / 3 innings into his big league career. The Rangers wish they had gotten that much out of Cristian Guzman.

“Ever since he’s come up, everything he’s done has been impressive,” Zimmerman said. “He trusts his stuff and he knows what he wants to do. If you have a plan, it doesn’t really matter where you’re at.”

Shortly after Roark’s promotion Aug. 7, Johnson came to believe Roark deserved to start. Ross Ohlendorf would not stop tiring after five innings, and Roark became the better option. He had punched up a 1.19 ERA as a long reliever. He needed only 13.8 pitches per inning, more efficient than any qualified starter in the majors. He fired his fastball up to 95 mph and peppered the edges of the strike zone.

“In spring training, I didn’t know his velocity was that good,” pitching coach Steve McCatty said. “But the thing that most impresses me is his command.”

“He hits his spots,” Johnson said. “It’s one thing to have good stuff. The best thing in the world is having that good command. He throws it like Satchel Paige. It’s his ‘B’ pitch – ‘It be where I want it to be.’ ”

Roark plowed through the Marlins in 19 pitches over the first two innings. He spotted his fastball on all four corners between 91 and 93 mph and he did not need much else. As the Marlins lineup cycled, he expanded his repertoire. He threw all four of his pitches for strikes.

“Vintage Tanner Roark,” Class AAA Syracuse Manager Tony Beasley said. “Command the ball. Attack hitters. No fear. It’s impressive. It’s good to see him come here and not skip a beat as far as his mentality, not shying away from big league hitters.”

Roark traced his success to last season. Earlier in his career, Roark allowed bloop hits and other misfortunes to rattle him. He concentrated last year on eliminating that.

“I became mentally stronger, and not let the little things get to me while I’m on the mound,” Roark said. “I would get myself amped up. I would tend to overthink. That’s when I’d start to nibble and not be as aggressive as I am now.”

“You could always see flashes,” Beasley said. “He would have one bad inning, and it kind of snowballed on him in the past. This year, it’s just a different focus. He’s very focused, determined. It’s just his mindset. We say a lot of times players come into their own. I think he’s at that point.”

Saturday night, Roark responded to his first sign of trouble with one of his best pitches of the night. Two singles gave the Marlins runners on first and second with one out in the fourth. To the plate walked Giancarlo Stanton. Roark fell behind with a slider. In a fastball count, catcher Wilson Ramos called for another slider. Stanton tapped it to second base, and Anthony Rendon started a 4-6-3 double play. Roark slapped his mitt and marched back to the dugout.

“He don’t shake me off too much,” Ramos said. “He just trusts me. He gets the ball. You put something down. He says in his mind, ‘Okay, I can do that.’ ”

Logan Morrison, who one night earlier had hit the longest homer ever at Marlins Park, whiffed at a backdoor breaking ball on the outside corner to strike out in the fifth. One inning later, Johnson pulled Roark. He had not thrown more than 64 pitches in a game since his call-up, and Johnson planned to limit him to 80. As Roark walked off the field, he saw family friends who lived in Florida holding signs repping his hometown, Wilmington, Ill.

The result had been cemented, but then it hardly mattered. The Nationals could spend days sorting out the reasons they failed to meet expectation. They can also start to answer questions, and it is worth finding out how much further Roark can come.

“I wasn’t trying to change anything, wasn’t trying to do anything different,” Roark said. “I was just throwing as hard as I can for as long as I can.”