PITTSBURGH — A brief mental lapse, or even two, can be the difference between a win and a loss. Just ask the Nationals, who had two minor mistakes in the first inning of Wednesday’s night game against the Pirates.

Over the next eight innings, they had ample at-bats and pitches to rectify their early missteps. And yet they never could quite do so in their 2-0 loss at PNC Park.

A quick glance at the box score wouldn’t indicate the Nationals (8-10) made any glaring mistakes. They finished with zero errors.

But, with two outs in the bottom of the first, Jake Irvin issued a walk to Bryan Reynolds. The blip seemed minor at the time. Three batters later, that proved not to be the case.

“Outside of the first inning, [Irvin] was really good,” manager Blake Butera said. “Unfortunately, he gets the first two guys out, which was awesome, and then the walk to Reynolds and then it kind of went from there. We just can’t give free bases.”

The Pirates’ next three hitters — Ryan O’Hearn, Marcell Ozuna and Nick Gonzales — all hit singles. They didn’t hit the ball hard, with exit velocities of 67.6 mph, 78.6 and 60.4 mph. And yet all of those weak hits equated to a 2-0 Pirates lead.

“First inning is what it is,” Irvin said. “When damage is happening on weak hits, you chalk that up to baseball.”

Gonzales’ infielder grounder should’ve ended the inning. But shortstop CJ Abrams took an awkward angle to the ball, took an extra shuffle and fired late to first. Gonzales beat the throw.

Butera said Abrams was caught between fielding the ground ball and touching second or charging the ball and throwing to first. Abrams hesitated. The Pirates extended the inning because of it. Yet it all started with the walk.

The Nationals, like every other team in baseball, are hoping to walk fewer hitters this season. They want their pitchers to attack the strike zone with their best stuff and make opposing hitters put the ball in play.

This has been the case in seasons prior as well. And it’s still a work in progress with the new coaching staff. With Wednesday’s loss, the Nationals pitchers have walked 87 batters, the fourth most in the major leagues. Often, opposing hitters have made them pay.

In Irvin’s last outing, he walked two in the first frame and then allowed a three-run homer. He had a similar fate thanks to his free pass on Wednesday. Still, in both instances, he kept the team in striking distance.

“He just does a great job of settling in and making adjustments off that inning, and then realizing like, ‘Hey, we have a chance,’” Butera said. “Just like in Milwaukee. Gives up three in the first and keeps us there, keeps us in the game. Same thing here.”

Irvin retired 12 of his next 14 hitters, though he walked Reynolds two more times before his night was over.

Reynolds’ third walk came with two outs in the fifth. Then O’Hearn singled. It seemed Irvin would face a similar fate as he did in the first inning. But he struck out Ozuna and yelled in celebration as he walked off the mound.

“We were just going to pitch to pitch,” Irvin said. “First inning, I would’ve liked to be more competitive in the Reynolds at-bat, but three weak-contact base hits, you just roll with the punches and keep going.”

Irvin varied his pitch mix each time through the order. His first time through, he relied heavily on his fastball, sinker and curveball. He used his changeup and slider more often the second time through. He mixed in his cutter more often his third time.

Even with the two-run deficit, the Nationals never mounted a serious comeback. They finished with only three hits and could not muster much offense against Carmen Mlodzinski, who entered in the second after an opener.

Mlodzinski threw six scoreless frames on 81 pitches. He didn’t throw more than 16 pitches in any frame. The Nationals finished 0-for-6 with runners in scoring position and left seven runners on base.

Butera and the Nationals hitters credited Mlodzinski for painting the edges. He rarely threw pitches over the heart of the plate. And when he did, the Nationals could not capitalize.

“It felt like, when we swung, maybe they were just off the plate,” first baseman Curtis Mead said. “When we didn’t swing, they were right just on the plate. I think it’s definitely a balance, and tonight we probably didn’t get it right.”

“You wait for a mistake, and it just didn’t seem like he made any tonight,” Butera said.

This article has been updated.