Ian Krol. (Jonathan Newton / The Washington Post)

The Nationals called up their first wave of September reinforcements on Sunday, the first day rosters expanded. Right-hander reliever Erik Davis and left-handed reliever Ian Krol were recalled from Class AAA Syracuse, while catcher Sandy Leon was called up from Class AA Harrisburg. Davis and Krol have already served stints in the majors this season, while Leon is making his first trip to Washington this season.

September call-ups don’t often see much playing time, as may be the case with the Nationals as they still hold out hope of making an improbable push for a postseason berth. But the relief arms, especially Krol, seem most likely to get the most work and could help lighten the bullpen’s load. Krol was optioned to the minors only 10 days ago because of a roster crunch, and in that span the Nationals were down to only one left-handed reliever.

Krol, 22, made an instant impact in the Nationals bullpen after he was called up originally straight from Harrisburg in early June. After a strong start, he struggled, posting a 5.40 ERA over his final 13 outings after the all-star break. The Nationals wanted Krol to use his brief time with Syracuse to iron out his mechanical issues. “Seems like a month [ago],” he said jokingly. Overall, he posted a 3.24 ERA in 27 major league games.

Krol found that he had struggled to put batters away in the majors with his curveball. He would jump ahead and then fire a curveball that would get mashed. He was leaving too many offspeed pitches up. In his five games with Syracuse, he felt an improvement in that regard. He buried his curveball low and in the dirt and hitters swung over them, instead of trying to hit the back part of the strike zone or leaving them over the heart of the plate.

“I wasn’t getting everything out of my delivery,” he said. “I wasn’t extending my arm as much as I wanted to. I was kinda cutting myself off which led to soreness [in my back] and sporadic locations where I’m throwing my pitches. I’ve been working on keeping my weight on my back shoulder when I load.”

Manager Davey Johnson used Krol often against left-handers during his first stint and figures to do that same again. Krol held left-handers to a .186 average, but was plagued by walks. Fernando Abad, the other left-hander, has allowed left-handed batters to hit .321 off him. With Krol in the fold, Tyler Clippard, who is lethal to left-handers, can be freed up to pitch in more important innings. Krol sees this final month as an opportunity to showcase his improvements and ability for next season, too.

“I’ve learned so much since I’ve been up here,” he said. “Being around guys that have been doing it for three, four years helps so much more. So I definitely want to finish strong, want to take whatever happens up here in the next month and bring it into the offseason, think about it and work on some things. I’m gonna take this next month as trying to learn but at the same time trying to have success.”

Davis, 26, provides Johnson another option out of an already right-handed dominany bullpen over the final month. He posted a 6.23 ERA in 4 1/3 innings in June with the Nationals, all the runs coming in one bad inning against the Mets on June 5. At Syracuse, he posted a 3.10 ERA in 45 games with a strikeout rate of 9.3 per nine innings, along with 15 saves. After his brief major league stint, Davis focused on improving his focus regardless of the inning he would pitch.

“When you’re coming in in a one-run game in the ninth inning — I was doing that down there — it’s easy to be all fired up and in control of things, but it’s not the way you come into every game,” he said. “So it’s taking that same approach, that same kind of fire into every outing, no matter what the scoreboard says. I kind of wanted to refine my whole approach, as far as going into each and every outing the same.”

Davis understands his role during this month.

“This team’s still in the playoff hunt,” he said. “Whether my job is to eat up innings, save the guys’ arms that are up here, that’s my job. Or whatever they ask me to do, it’s to go out there and put up a zero, more than anything. That’s what I’m going to try to do. Soak up as much from all the other guys who have been doing it much longer than I have.”

Barring any injuries, Leon, 24, may see the least amount of playing time. This final month will be more of a chance for him to learn from the experience and work with the major league coaches to improve his hitting, especially Rick Schu, who he has worked with in the past. Leon struggled all season at the plate, hitting .177 with a .542 OPS at Harrisburg. Last season, the switch-hitter hit .322 with a .856 OPS across three minor league levels.

He is regarded as the top defensive catcher in the minor league system, but he understands he needs to snap out of his season-long hitting slump. The problem, he said, hasn’t been mechanical but with his approach. He was, in fact, surprised he was called up as he expected to stay with Harrisburg for the playoffs.

“Sometimes too aggressive at pitches and you’ve got to be smart, too,” he said. “So I think just to calm down in the game and just relax and see what happens. All year I’ve been struggling all year so I’m feeling better here.”

More players are expected soon. The Nationals were planning to call up three pitchers and four or five position players. Infielder Zach Walters, outfielders Corey Brown and Eury Perez, and utility man Jeff Kobernus are the likely position player call-ups and are expected later.