Nationals beat writer Adam Kilgore talks about whether Ryan Zimmerman will eventually return to third base when he rejoins the team. (Post Sports Live/The Washington Post)

Before each pitch Monday night at Class A Potomac, Ryan Zimmerman took one small step forward with his left foot, bent at his waist and extended his glove — ready position at the hot corner. He instinctively broke on all contact, even balls fouled to the backstop. His movements were notable because he was playing left field. Old habits are hard to break.

On the first 1,120 occasions Zimmerman took his position on a major league diamond, he jogged to shortstop once and to third base the other 1,119 games. Tuesday night at Nationals Park, he will probably return to the Washington Nationals after missing 44 games on the disabled list with a broken thumb. And he will probably play left field.

“Whenever you do something new, it’s a little nerve-wracking,” Zimmerman said. “But I feel like I can go out there and do what I need to do.”

After three weeks of practice and three Class A tuneups, Zimmerman’s franchise-shifting switch will likely become vividly real. Zimmerman had not been told he would face the Philadelphia Phillies, but he planned to return Tuesday to Nationals Park if everything went well. And everything went well.

Monday night, in his final minor league rehab game, Zimmerman went 2 for 4 with two singles and scorched a lineout to deep center. Once Zimmerman reached base, he wore a padded, fingerless black glove over his right hand to protect his thumb, which he said is at full strength, and does not even swell anymore. Always quick to recapture his eye and timing, Zimmerman finished his rehab appearance with five hits in 14 at-bats.

In left field, Zimmerman made a smooth, easy catch on a can of corn near the left field line. He had no other action in left, unless you count the light trot he made to the warning track, watching a home run fly into the trees beyond the fence. Or the ball a fan threw onto the field, which Zimmerman tossed back into the bleachers.

He played three games in left field at Potomac, and each game it felt less foreign to Zimmerman. His lack of experience worried him, but he felt confident he could field balls and hit cutoff men with enough proficiency to keep his powerful bat in the lineup.

“I feel like I can be adequate and do a good job,” Zimmerman said. “I feel like I can do things to help us win. I think that’s the most important part.”

After Zimmerman broke his thumb April 12 and went on the disabled list the next day, the Nationals went 20-24 and scored 3.7 runs per game. They have played all season with holes in their lineup, but once Zimmerman returns Bryce Harper will be the lone regular remaining on the disabled list.

“We’re just excited for him to come back,” center fielder Denard Span said. “He’s a big part of this team, and a big part of our lineup. We definitely missed him. I can’t wait for him to get back, just to add that extra presence.”

Zimmerman’s familiar presence will be there in new form, with him in left field. Zimmerman has dived into the new position headlong. Monday afternoon, Zimmerman arrived at Pfitzner Stadium not long after noon. At 2 p.m., he trotted to left field. Nationals first base coach Tony Tarasco and minor league outfield coordinator Gary Thurman stood in the infield. They fed balls into a machine that spit them into the air for Zimmerman to track down.

“He looks comfortable,” said Potomac Manager Tripp Keister, a former minor league outfielder. “That’s the part that really stuck out to me. He wasn’t fighting it at all. He’s played on the left side of the diamond his whole life, so seeing balls off the bat really wasn’t an issue for him. I would be very surprised if he’s not a very good outfielder here soon.”

The larger question may be how well Zimmerman adjusts to making throws from the outfield with his battered, chronic right shoulder. Two rival scouts in Potomac said they believed Zimmerman would have an easier time throwing from the outfield than from third base.

“It’s a different throw,” Zimmerman said. “I can get my momentum going. I can use my legs a lot more. A lot of the times, unless the ball comes right to me, it’s going to be just getting the ball to the cutoff man, letting him do the job. As far as practicing the throws I need to make, I’ve practiced those and I’ve made them all.

“I’m not going to be [Yasiel] Puig or anyone like that. But not too many people are.”

Zimmerman expressed confidence his throws would require less precision, and he would have more time and space to gather momentum with footwork, and need to rely less on his arm.

“You have to be so much more accurate in the infield,” Zimmerman said. “The timing is different – you have usually less than four seconds to react to a ball, catch the ball, set your feet and throw the ball over 100 feet. People don’t realize how quick that happens. In the outfield, you have a lot more time. You can situate your body a little bit better. Those are all things that I’m still learning. But I can use those to my advantage.”

Now, likely starting with the Phillies on Tuesday night, major league base runners will have the opportunity to test Zimmerman in a new way. Is he up for the challenge?

“They should run all they want,” Zimmerman said.