Jose Marmolejos poses during media day before the 2017 season. (Photo by Toni L. Sandys/The Washington Post)

The Nationals grouped Jose Marmolejos with their lesser prospects when they signed him for $55,000 in 2011 because, frankly, he wasn’t considered a high-ceiling talent. He signed with the organization in the Dominican Republic at 18 years old — older than most Dominican signees — only after he went undrafted after graduating from high school in Florida. He was a first baseman with limited mobility and power.

Six years later, Marmolejos is the Nationals’ reigning two-time minor league player of the year, which prompted the organization to add him to its 40-man roster last fall, and he continues to hit. After posting an OPS of .848 and .845 between three levels the last two seasons, Marmolejos, who began the season on the 60-day disabled list with an elbow injury, entered Monday with a .386/.438/.614 slash line in 14 games for Class AA Harrisburg.

At 24, he’s on the older end of the prospect spectrum and has just 47 games of experience in AA, but he hasn’t stopped hitting and reaching the big leagues is a near certainty if he stays healthy.

“He’s a professional hitter,” Nationals director of player development Mark Scialabba said. “He’s very consistent from at-bat to at-bat. He has a repeatable swing. Short, compact. Can hit the ball to all fields. And does a nice job of staying poised in the box. He understands the strike zone.”

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Last month, as he compiled at-bats in extended spring training in Florida, Marmolejos didn’t look like someone who was about to head north and go on a tear. His at-bats were good, but the results weren’t. Results, however, are irrelevant in that environment, where young pitchers have trouble commanding pitches consistently, leaving hitters to fish for production. The process was key and it has translated to the eye-popping production with Harrisburg.

“It can be monotonous at times,” Scialabba said. “It can be tough to get the adrenaline going compared to what it would be up north over a full season.”

Marmolejos immediately produced when he got to Harrisburg and hasn’t stopped. He reached base safely in each of his 14 games entering Monday and had a hit in 12 of them, including five in one game against Erie on May 22. The next step in his development, Scialabba said, is his power and he has exhibited more of it pull side this season with three home runs and four doubles in 64 plate appearances entering Monday.

Defense isn’t Marmolejos’s strength. As a left-hander, he’s already limited, but the Nationals have moved him to left field for the past four games, including Monday. The additional positional versatility adds to Marmolejos’s value — and could potentially open another avenue to the big leagues.

“He wasn’t among the top group of prospects that we had and he really put himself in that position by really working hard and showing his ability to barrel the baseball on a consistent basis,” Scialabba said. “That’s what really separated him once he got the opportunity to play more for us. He’s a professional hitter that will give you a great at-bat. He’s earned his way to this point. He’s becoming a prospect with what he’s done on the field.”

— Chris Heisey joined Marmolejos in Harrisburg’s outfield Monday as he began a rehab assignment after rupturing his biceps tendon last week. Heisey played right field and went 0 for 2 with a strikeout.

— A day after trading for veteran outfielder Ryan Raburn and sending him to Class AAA Syracuse, the Nationals signed 29-year-old right-hander Sean O’Sullivan to a minor league deal and also sent him to Syracuse. O’Sullivan began the season in South Korea, where he allowed 14 runs on 17 hits in eight innings. He last pitched in the majors with the Red Sox last season and posted a 6.75 ERA over 21 1/3 innings in four starts and one relief appearance.