Bryce Harper is doubled off of first base in the Nationals’ 1-0 loss against the Reds, one of two outs he made on the base paths Saturday. (Joe Robbins/Getty Images)

In perhaps the most important moment of Saturday’s 1-0 loss to the Cincinnati Reds, Bryce Harper hunched over in the batter’s box, his shoulders square toward the mound and his bat held by both hands. The best left-handed reliever in baseball, closer Aroldis Chapman with his firebreathing fastball, stood on the mound. Down by a run and with the potential tying run at first base, Harper looked ready to drop down a sacrifice bunt to get Ian Desmond into scoring position with no outs in the ninth inning.

Instead, Harper pulled the bat back, a peculiar designed play by Washington Nationals Manager Matt Williams. Desmond took off for second base and, despite Chapman’s slower time to home plate, catcher Brayan Pena threw Desmond out after catching Chapman’s 101-mph fastball. Harper then took the next pitch, a fastball over the plate, to strike out looking and the crowd erupted. “He throws 103,” Harper said. “I kind of had no shot.”

After the next batter, the game was over. The Nationals didn’t fall to the Reds solely because of the odd ninth-inning sequence, but it was one of a handful of mistakes, including two base running gaffes by Harper, that spoiled a terrific pitchers’ duel between Nationals starter Gio Gonzalez and Reds all-star Johnny Cueto. Williams’s call from the dugout for the fake bunt also sparked questions afterward.

The Nationals knew Chapman’s delivery typically takes 1.6 seconds, a slow time, and thought they had a chance for Desmond to move into scoring position. Although Harper tried to bunt on his own in the first pitch of the at-bat, he was signaled from the dugout to try the fake bunt. Chapman threw over to first base twice, but not before the designed play.

“We’ve got an opportunity there to get a guy in scoring position, so we’ve run it a few times this year,” Williams said. “It’s worked. [Desmond] didn’t get the greatest jump. But that’s a designed play that we work on. And the fact that [Chapman is] slow to the plate, we wanted to take a chance there.”

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)

For seven innings, Gonzalez and Cueto matched each other except for the lone run scored off Gonzalez. Cueto started off slow, allowing the leadoff hitter to reach base in four of the first five innings, but he escaped every jam. He had nine strikeouts, gave up only four hits and survived three walks. He toyed with batters with his array of speeds and movement. The few Nationals who reached base against him needed to try to take advantage and score. None did.

Harper’s first out on the base paths was understandable. Harper drew a walk against Cueto to start the second inning. Although he has struggled to find a comfortable stance and feel at the plate, Harper still has managed to draw walks. The next batter, Wilson Ramos, crushed a ball deep to the right-center field gap that appeared destined to score Harper.

But Jay Bruce, among the game’s best right fielders, chased down the ball and made a terrific running catch. By then, Harper was already around second base. Bruce fired a throw back into the infield, and the relay throw cut down a sliding Harper at first base.

“I thought that was burned for sure,” Harper said. “Guys hit balls like that in this yard all the time and [the ball] usually hits off the wall or leaves the yard. There’s nothing I can do about it. Definitely would have scored if it was over his head. Bruce made a great play, came up firing.”

Harper’s second out on the base paths, however, needlessly killed a potential rally. After Harper drew a one-out walk in the seventh, Ramos hit a slow groundball toward third base. Ramon Santiago raced in and fired to first too late to get Ramos, while Harper kept running and tried to go to third. Third base coach Bobby Henley held his left hand to stop Harper. First baseman Todd Frazier threw the ball to shortstop Zack Cozart, who started a rundown to catch Harper.

“I thought I had a beat on it, but they got me,” Harper said.

“Certainly if the ball gets away from the first baseman or there’s an errant throw he can make it, but he didn’t have a good enough jump,” Williams added.

Had Harper not been caught late in a one-run game, the Nationals would have had two men on with at least two shots — No. 8 hitter, Kevin Frandsen, and likely a pinch hitter — to drive them in. Instead, Frandsen hit a flyball to right field to end the inning. The base running outs loomed large in the close game, but Williams brushed off their effect.

“It’s part of our DNA: We’re going to be aggressive,” Williams said. “So sometimes it works. We talked about it not too long ago, how good it was. Sometimes it bites you. We can’t change the way we play. It’s aggressive by nature, it’s the way we want to go about it, and we don’t want to change that.”

For the most part on Saturday, Gonzalez was sharp, in control and efficient. His fastball sat around 93 mph. His secondary pitches, which have powered him over the past month, were strong.

“I tried to take a little page off Tanner Roark and Doug Fister’s method of pitching or working quick and pounding the strike zone,” Gonzalez said, “and not try to baby the pitches and just try go out there and try to do your best and throw strikes.”

In the fifth inning, Chris Heisey hit a well-placed inside fastball to left field for a ground-rule double. Gonzalez then got Skip Schumaker to fly out. But with Pena batting, Heisey stole third base. With the infield in, Pena drilled a curveball to left field for an RBI single.

“Every run is pretty crucial, and that’s not the case in every game,” Nationals first baseman Adam LaRoche said. “Games like that you got to take advantage of every mistake and do it carefully if that’s possible so you don’t run into outs. Always got to be heads up, but especially in games like this when you know there’s not going to be a lot of runs.”

After Harper’s second base running mistake, the Nationals threatened again with two outs in the eighth inning when reliever Jonathan Broxton walked Anthony Rendon and then hit Jayson Werth on the left shoulder with a pitch. Reds Manager Bryan Price called for Chapman to try for his first four-out save of the season.

Chapman’s first pitch to LaRoche, a 100-mph fastball, nearly sailed past Pena, but the catcher kept it nearby. LaRoche got into a 2-1 count but then hit another 100-mph fastball to shortstop Cozart for the inning-ending groundout. An inning later, the Nationals’ promising start to the ninth inning against Chapman ended in frustration.