Ryan Zimmerman returns from the 15-day disabled list by striking out four times to earn the dubious golden sombrero. He was more effective outside the batter’s box, fielding three balls and making strong throws on all of them. (Justin K. Aller/Getty Images)

Adam LaRoche reached into his first baseman’s mitt to pull out the ball, an act so reflexive for a baseball player it warrants no thought, like breathing. LaRoche, surely, would grab the ball and fire it to second base to complete Ross Detwiler’s pickoff. The Washington Nationals would dash off the field, still tied after the fifth inning, and try to conjure runs from their impotent bats.

Given the current state of the Nationals’ offense, any moment may be magnified, and at any time a game may unravel. In the Nationals’ 3-1 loss to the Pittsburgh Pirates on Friday night at PNC Park, a mindless task turned into a pivotal moment. LaRoche fumbled the exchange, the inning lived on, and Detwiler surrendered a game-breaking, two-run home run to Jordy Mercer, a second baseman who a few hours earlier had been an Indianapolis Indian.

In different conditions, LaRoche’s bobble may have been forgotten, lost amid Andrew McCutchen’s continued bludgeoning of the Nationals and the return from the disabled list of Ryan Zimmerman, who went 0 for 4 with four strikeouts and, more happily, made strong throws after all three balls hit to him. Currently, though, the Nationals’ dearth of runs makes every play a potential hinge.

On Friday, the Nationals struck out 14 times, seven of those looking, nine in seven innings coming against Pirates right-hander A.J. Burnett, who became the latest starter to steamroll the Nationals. They have, among other assets, a base-clogging leader in Denard Span, a generational slugger in Bryce Harper and an all-star shortstop in Ian Desmond. So far, the assembled talent has added up only to one of the league’s least productive offenses.

“We’re kind of hitting rock bottom,” Manager Davey Johnson said. “We just need to man up. Let’s go. Let’s start doing things we’re capable of doing.”

The Post’s Jonathan Forsythe says we should be worried about Stephen Strasburg’s pitching arm after his start on Monday night. (Post Sports Live)

They have scored three runs or fewer in 12 of their past 15 games, including the last six. The Nationals finished Friday night with a collective .669 OPS and a .291 on-base percentage, both better only than the woeful Miami Marlins in the National League. Their 3.4 runs per game ranked third-worst in the majors. The team-wide slump prevented the Nationals from capitalizing on the momentum gathered from dominant starts by Jordan Zimmermann and Dan Haren.

Johnson was particularly perturbed by the Nationals’ seven strikeouts looking. He wanted his hitters to show more aggression early in the count, and to show more discipline on balls out of the zone. Shortstop Ian Desmond gave Burnett credit — “he pitched a really good game,” Desmond said — but Johnson thought the Nationals could have used a better approach.

“He had a fastball that was coming back over the plate,” Johnson said. “Guys were giving up on balls away. We’ve got to make adjustments. We’ve got a lot better hitters than we’re showing.”

If there is hopeful sign, it is that the Nationals have been here before. After 30 games last season, the Nationals possessed a .664 OPS and had scored 102 runs – precisely the same number as this season. The difference? After a red-hot start, those Nationals had settled at 18-12. These Nationals have wobbled to 15-15.

“Looking back, we went through this for a lot of the year,” LaRoche said. “It seemed like we were not doing a ton offensively, but we were winning ballgames. So, right now, it’s magnified.”

The Nationals have an even more difficult time scoring runs when Harper, their engine, may not be himself. Tuesday night in Atlanta, Harper had bruised his left side banging into the outfield fence. Wednesday, pain after a check swing forced him to leave the game. He brushed off any effects, but since the collision he has gone 1 for 12, including a strikeout in the eighth inning against Mark Melancon with two on and two out.

The Nationals scored their lone run Friday in the fourth inning with a sudden two-out rally. LaRoche drew a walk. Tyler Moore, starting in place of Jayson Werth, lined a single to center fielder. Danny Espinosa rolled a single through the right side, enough to score LaRoche from second before Moore was thrown out trying to go from first to third.

Detwiler operated with the score tied as the game churned into the fifth. Starling Marte singled with two outs, a seemingly harmless hit, just the fourth Detwiler had allowed all game. With Mercer at the plate, Marte bolted for second on Detwiler’s first move. Rather than throwing plateward, though, Detwiler extended his right leg and threw to LaRoche. They had Marte trapped.

LaRoche stepped forward to give himself a better angle as he brought the ball out of his glove. But he never gripped the ball, and he never threw it. Marte slid in, safe, and the inning continued.

“I knew with a high, slow leg kick on that particular pick off, I knew I had one shot,” LaRoche said. “Catch it, snap throw hard, try to make the throw. I just wanted to get it, and I couldn’t find it.”

Still, Detwiler needed only to handle Mercer. The Pirates had called him up from Class AAA Indianapolis on Friday afternoon to replace usual starter Neil Walker. Mercer, 26, had hit 42 home runs in 2,247 career minor league plate appearances.

“I looked at who I had at the plate and thought I had a good chance if I could just get ahead of him,” Detwiler said.

Detwiler, though, fell behind with two balls. He tried to get back into the count with a fastball over the outside corner, but he mistakenly “cut” the pitch, and it tailed back over the plate. Mercer pummeled it over the fence in left field.

“A professional hitter hit a home run,” Detwiler said. “That’s what he’s paid to do.”

McCutchen had given Detwiler his first trouble with an upper-deck, solo home run in the first inning. The outfielder constitutes one of baseball’s brightest talents. He is not the greatest player who ever picked up a bat, but how many Nationals fans could be convinced otherwise? In 24 career games against Washington, McCutchen has hit 11 homers with a .456 batting average.

“He’s not going to hit a home run every time,” Detwiler said. “It seems like against us, he does.”

The Nationals could have overcome McCutchen’s blow. If and when their offense clicks, they will have the leeway for a ball to get stuck in a glove. On nights like Friday, though, it can mean the difference between a victory and another loss.

“Fun game,” LaRoche said. “Isn’t it?”