The Post Sports Live crew debates whether the Nationals should make a move to add a missing piece or stand pat before the July 31 trade deadline. (Post Sports Live/The Washington Post)

Great American Ball Park isn’t meant for pitching, especially during the humid summer months. A ball need only travel 325 feet down the right field line or 328 feet down the left field line to reach the fence. Balls hit hard in the air have a chance to leave the yard. But this stadium hadn’t met the likes of Doug Fister until Sunday.

Of all the starters who took the mound here this weekend, in matchups fit for a fall series, Fister delivered perhaps the finest performance, a continuation of his brilliant season. Pitching in Cincinnati’s bandbox for the first time in his career, Fister mowed through the Reds’ lineup with ease. He filled up the strike zone, gave his defense plenty of groundballs and fired seven scoreless innings in a 4-2 win.

Fister gave up only three hits en route to becoming the fastest pitcher in Nationals history to reach 10 wins, which ties Tanner Roark for the team lead. Take out his rough Nationals debut, and Fister has a 2.30 ERA over his past 86 innings. His dazzling pitching over the past three months helped keep the Nationals’ lead in the National League East at 11 / 2 games over the Atlanta Braves, who won Sunday evening at San Diego.

“You feel good when Doug is on the mound,” right fielder Jayson Werth said. “He works fast and throws strikes. He’s been one of our best all year. With him out there, throwing pitches like the way he did [Sunday], and we give him a run or two, he’s going to hold on to it.”

Tyler Clippard pitched a scoreless eighth inning, and Rafael Soriano notched his 200th career save after Aaron Barrett injected drama into the ninth. The Nationals’ stout pitching this series mostly neutralized a place meant for offense. Capped by Fister, Nationals starters allowed only two runs over 21 innings in the series. In this stadium’s 12-season history, there has never been a three-game homerless stretch until now.

“It’s never easy here,” Nationals Manager Matt Williams said. “I liken this ballpark to Colorado. It’s small. We had a little different weather. Some wind blowing in. There were a couple balls that were hit pretty good that didn’t go anywhere. Nonetheless it’s small. Our guys pitched well. So did theirs.”

The Nationals claimed their fourth straight series win with the help of an offense that did just enough, sparked by Werth’s bases-loaded walk in the fifth inning and Adam LaRoche’s two-run single one batter later.

Reds right-hander Mat Latos didn’t allow his first hit until the fifth inning, when Danny Espinosa laced a leadoff single to center field. Espinosa advanced to second base with one out when Fister laid down a sacrifice bunt. Denard Span, the Nationals’ hottest hitter of late, then drew one of his four walks.

Latos then hit Rendon in the back with the second pitch of the at-bat. Up came Werth, with only one hit in his previous seven at-bats in the series. He fouled off the first pitch and then took a called strike on the inner edge.

“In that situation, you can’t give in,” Werth said. “We’ve been battling. Up to that point, we really hadn’t done a whole lot.”

Werth needed to salvage the at-bat. Ball one was way high. Ball two was a curveball that just missed the outside edge and prompted boos from the crowd and an eye roll from Latos. He then tried to go inside again but missed twice. Werth tossed his bat to the side and took first base. It was Werth’s first walk after falling behind 0-2 since 2012. It gave the Nationals a 1-0 lead and their first run since the sixth inning of Friday’s game.

“The extension of that inning is big,” Williams said.

LaRoche then added the hit — a two-run single to left field — that gave the Nationals and Fister a more comfortable cushion. Fister did the rest.

Fister thrives on tempo and command, and both of those traits were in top form against the left-handed-heavy Reds. He needed only 37 pitches to get through the first three innings, and he threw only seven balls in that span.

At times, Fister’s sinker looked unhittable, dropping hard and late as it reached the plate. Reds mashed them into the ground, producing 11 groundouts. His change-up stood out, too. Fister walked only one batter and struck out five. Sparkling defensive plays by Ian Desmond and Anthony Rendon robbed hits.

“Everybody was giving everything they had,” Fister said. “That’s why we’re playing well together and having some success.”

Fister’s only jam, if it can even be called that, was minor. He gave up a one-out single to Devin Mesoraco in the seventh inning and then fielded a mound visit from pitching coach Steve McCatty. Fister then fired more sinkers at Jack Hannahan for a fielder’s choice groundout and struck out Donald Lutz with his curveball.

Fister bounced off the mound and pumped his fist as he walked toward the dugout. With catcher Jose Lobaton behind the plate, Fister has a 1.82 ERA over eight starts.

“We [are] almost on the same page all the time,” Lobaton said.

Rendon added an RBI single in the ninth inning that gave the Nationals a 4-0 cushion, enough to withstand the minor drama of the bottom of the inning. With a four-run lead, there was no save situation, so Barrett stared the frame. But he gave up two singles, and Williams turned to Soriano to escape the two-on, no-out jam.

Soriano gave up a two-run double to the first batter he faced, Mesoraco, runs charged to Barrett, and the tying run came to the plate. Soriano struck out Hannahan and got a groundout out of Lutz and a flyout from Chris Heisey to end the game. He became the 46th reliever to reach the 200-save milestone.

“I be happy for that because it’s not something too many people have,” Soriano said.

On the field, Soriano untucked his jersey and Fister celebrated another win with his teammates.