Tanner Roark pitches seven innings, giving up only three hits and one run. (Jamie Sabau/Getty Images)

Nearly four full months into the season, the pitcher who fought for the final spot in the Washington Nationals’ rotation in spring training stands ahead of them all. Tanner Roark, the unassuming, unheralded starter who blossomed late, has long moved past any fluky hot streak. After a masterful start in Friday’s 4-1 win over the Cincinnati Reds, Roark’s body of work is large enough to prove he not only is a major league starter but a gifted one, too.

Roark fired 93-mph tailing fastballs past helpless Reds hitters. His sinking fastballs induced weak contact, broke bats and ate up innings. His improved slider fooled batters. Combined with his savvy and guile, Roark fired seven superb innings against the Reds, giving up only one run on three hits. His pitching pushed the Nationals to 21 / 2 games ahead of the Atlanta Braves atop the National League East standings.

In late July and on a rotation with big name starters such as Stephen Strasburg, Jordan Zimmermann, Gio Gonzalez and Doug Fister, Roark has the staff’s best ERA among starters and the 10th best in the National League at 2.82. He also leads the Nationals with 10 wins. The pitcher who pitched in independent baseball before he was drafted, who was picked up by the Nationals in a minor trade and didn’t reach the majors until he was 26 has been the Nationals’ most consistent pitcher since the start of the season.

“It’s unbelievable to be honest with you,” Nationals center fielder Denard Span said. “You got to give him all the credit in the world. He’s solidified our rotation. We’ve got the big guns, the big names, and they’ve earned a lot of respect. But you’ve got to give him a lot of credit for being at the back end of the rotation and doing what he’s done.”

Roark is nearing a full season in the majors. He was called up Aug. 6, 2013, after he finally figured it out at Class AAA Syracuse. Since then, he has a 2.43 ERA. Over the last calendar year, his 2.67 ERA as a starter entering Friday was tied for fifth in the majors (minimum 150 innings). Ahead of him? Clayton Kershaw, Johnny Cueto, Zack Greinke and Jon Lester, all of them all-stars and two of them past Cy Young Award winners.

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“We saw it last year,” Manager Matt Williams said. “Everybody was waiting for it to go the other way. But it hasn’t. He’s just continued to work hard and pitch well and compete. We’re proud of him.”

“It’s pretty cool just to think about,” Roark added. “It’s been my dream ever since I was a little kid to be in the big leagues. Got the chance last year and took the opportunity and tried to run away with it.”

Early in Friday’s start, it was clear Roark had some of his best stuff of the season. In the second inning, he froze Jay Bruce on a wicked 94-mph cut-back fastball on the inside edge. Three innings later, he used a change-up to make Devin Mesoraco look silly on a swing after firing two hard sliders. Roark induced a heap of groundouts and was in control from the start. He used only 94 pitches to notch 21 outs.

Roark has “the ability to throw any pitch in any count for a strike,” Williams said.

Even with the lineup’s loss of Ryan Zimmerman, who has been out since he left Tuesday’s game with a hamstring injury, the Nationals’ offense has not let up. The Nationals have reached double digits in hits in their last eight games. They left 12 on base but smacked 12 hits Friday and chased Reds starter Alfredo Simon, an all-star who entered the game with a 12-4 record and 2.74 ERA, in the fifth inning.

Rookie Zach Walters, a switch-hitting infielder who primarily has played shortstop in the minor leagues, rewarded Williams’s faith in starting him at second base for the first time in the majors. Walters’s double in the fourth inning off Simon started the Nationals’ scoring outburst and gave them a 1-0 lead when Bryce Harper scored.

Span, who notched his second straight four-hit game, made it 2-0 with an RBI single to right but was thrown out between first and second base. Anthony Rendon added to Simon’s misery with a first-pitch RBI single to left that increased the Nationals’ lead to 3-0.

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The Reds’ lone run against Roark came in a hard-luck fourth inning. He gave up a leadoff single to Billy Hamilton, who stole second and took third on a groundout. With two outs, Roark got Ryan Ludwick to hit a soft, check-swing grounder to the right of the mound. Roark dived for the ball and deflected it, and Walters couldn’t flip the ball to first base in time. Hamilton scored, but Roark escaped the inning without further damage.

“If he doesn’t dive for that ball and deflect it, he may have not given up any,” Williams said.

In the sixth inning, Harper made a slick, diving, backhanded catch in left field to rob Hamilton of a hit. After the catch, Harper was slow to get up. Harper missed two months earlier this season after surgery on his injured left thumb, and that’s what hit the ground hardest when he made the catch. As Williams and a trainer jogged out to left, Harper waved them back. They returned after a quick visit, and Harper remained in the game.

Williams described Harper as suffering a “stinger” but said he is “fine” and had “no issues.”

In his final inning, Roark minimized damage in his trademark fashion. He hit Mesoraco with a pitch and then gave up a soft single to Brayan Pena. The tying run, Zack Cozart, came to the plate, and pitching coach Steve McCatty came to the mound. Little rattles Roark, so he regrouped and got Cozart to hit a groundball to third baseman Rendon, who made a stellar diving play to end the inning.

In the dugout, Roark slapped hands with teammates. He would be lifted for a pinch hitter in the next inning, another chapter in a stellar season and a start to a career that has surprised even him.

“I have all the confidence in the world in myself and my team,” he said. “It’s been a good ride so far. Keep it going.”