First baseman Chris Marrero, shown throwing during infield drills in February, has shown noticeable improvement on defense. (Jonathan Newton/WASHINGTON POST)

On Monday afternoon, Chris Marrero shuffled to his right, fielded a tricky chopper and made an easy, overhand toss to hit Jason Marquis in stride as he covered first base. Later, he smoothly scooped a one-hop throw by Ryan Zimmerman, securing a double play.

For most any other first baseman on a major league diamond, the plays would have hardly drawn notice. For Marrero — once the brightest piece of the Washington Nationals’ future — they represented the primary reason why the Nationals no longer believe his defense will be an impediment to his reaching the major leagues.

“He worked his [rear end] off for two years,” one Nationals official said.

In his first major league camp, Marrero has impressed Nationals brass with his improved defense at first base, where he made 38 errors over the past two minor league seasons. Let’s not overstate things: Marrero has not turned into a standout defensive player. But, for Marrero, that was never the point. He used to be a liability. Now he’s an adequate major league first baseman.

“I’m very comfortable with him over there defensively,” Nationals Manager Jim Riggleman said. “He’s really made strides with his range. He throws the ball very well when that’s needed from a first baseman. His hands are soft. He’s a very usable first baseman. There was some question as to whether he was going to be able to do that. There’s no question now.”

Marrero, the 15th pick of the 2006 draft, has endured enough plot twists in his career that it is easy to forget he is still just 22 years old. The Nationals drafted him as a third baseman and immediately converted him into a corner outfielder. By the end of 2007, they decided he didn’t have the speed and moved him to first base.

By that point, his lack of a position didn’t matter. Splitting 2007 between Class A Hagerstown and Class A Potomac, at 18, Marrero hit 23 home runs and slugged .484. Baseball America ranked Marrero the Nationals’ top prospect and the 27th best in baseball. In 2008, after converting to first base, Marrero slumped to start the season, hitting .250 before he slid into home plate, broke his right fibula and tore ligaments in his right ankle. Marrero had just begun playing first base, and now he would virtually have to start over.

Through it all, the same theme persisted. Marrero precisely fit the mold of a prospect his team drooled over when he stood in the batter’s box but wanted to hide when he put on a glove.

“That’s what everyone says,” Marrero said. “According to me, I think I’m good at both aspects of the game. I work on both sides of the game.”

In 2009, Nationals reliever Drew Storen played with Marrero from July until the end of the season at Potomac. Asked about Marrero’s defense at that point, Storen said, with a half-smile, “He had a great bat, right?” When Storen opened last year in Class AA Harrisburg, he noticed a difference in Marrero.

“You can tell he’s put in the effort,” Storen said. “You can definitely tell he’s made some improvements. It would be easy for him to say, ‘Well, it doesn’t matter, I hit so well.’ He’s done the right things and made the right strides to get there.”

Marrero, though, had not yet become an adequate first baseman. He would sometimes drop seemingly routine throws. He totaled 18 errors, and he knew he could have eliminated them.

“I made dumb mistakes last year,” Marrero said. “I sometimes got a little lazy. You realize as games go by, you’ve just got to be ready every pitch. That’s what I’ve learned, too: Expect the ball every time.”

This winter, the Nationals added Marrero to their 40-man roster. A step closer to the majors, he wanted to prove he belonged. He took hundreds of groundballs every day with his brother, Christian, a Class AAA outfielder for the Chicago White Sox. Marrero added muscle and enhanced his speed.

“I don’t think I’m doing anything different,” Marrero said. “It’s just the confidence. I have the confidence I’m going to catch the ball. I bust my butt every day taking groundballs, but at the end of the day it’s all about knowing you can catch the ball.”

The Nationals signed Adam LaRoche this offseason to a two-year contract, effectively blocking Marrero for now. Still, it has been his goal every year to make the majors, and this is the first in which it stands as a realistic possibility. Marrero could start the season with Class AAA Syracuse, and if LaRoche is hurt or the Nationals deem Marrero ready for a September call-up, Marrero could play in the majors this year.

“It’s a goal of mine to get called up,” Marrero said. “I’ve gotten a lot better. I want to get to the point where one day if I play with Zimmerman, if I play with all these guys, that they can just throw the ball over there and not worry about me catching the ball. That’s the confidence I want to have.”