PHOENIX — After 23-year-old Andrew Stevenson met reporters before his first major league game, when the camera turned off and he got down from the top of the bench in the visitors’ dugout, Stevenson moved out toward the dugout steps and looked around.

“Nice ballpark,” he said, smiling at his understatement. Not 18 hours before, Stevenson was playing in a Class AAA game in Columbus Ohio. One early morning direct flight to Phoenix later, the Nationals’ first pick in the 2015 draft was in the big leagues.

Stevenson to join the Nats in Arizona

Stevenson’s first big league assignment was born out of unexpected — and frankly, unbelievable — outfield need. With Michael A. Taylor and Jayson Werth out, the Nationals were relying heavily on Brian Goodwin, Bryce Harper, Ryan Raburn and Chris Heisey. No other outfielders on their 40-man roster were healthy.

Raburn left the team Sunday for bereavement leave after the death of his grandfather, something the Nationals planned for by calling up Pedro Severino to take his place. Then Heisey strained his groin in Saturday night’s game, something the Nationals had not planned for, an incident that sent General Manager Mike Rizzo into Dusty Baker’s office for 15 minutes or so right after the game.

“We called Doug Harris, discussed it for five minutes and made a decision,” Rizzo said. “These decisions aren’t made in a vacuum. We put a lot of time and effort and conference calls and meetings into what we’re going to do if this happens. We’re prepared for just about everything.”

Stevenson, however, could not have been prepared for the phone call he got after his game. It came from a number he did not recognize, that of his Class AAA Syracuse Manager Billy Gardner, who told him the Nationals needed him.

“You kind of don’t know if it’s real at first,” Stevenson said. “Your heart’s kind of pounding.”

Stevenson was in major league camp with the Nationals this spring, and impressed by hitting .333 and playing strong defense in 15 games. He began the season in Class AA Harrisburg, where he hit .350 in 20 games before jumping to Syracuse. A month into his Chiefs tenure, Stevenson was hitting .171. A month later, he was hitting .255.

“I sped the game up on myself,” said Stevenson, known as a high-energy, strong-work-ethic type.  I wanted to make a good impression and ended up pressing too much. Was able to work out of that.”

“He’s shown in the past, it takes him a while at each level to make an adjustment, but he makes the adjustment,” Rizzo said. “He’s got the ability to be able to play here in the big leagues. Plus defender in three outfield spots, he gives you a left-handed bat and speed off the bench.”

Stevenson isn’t used to a reserve role, but Diamondbacks all-star lefty Robbie Ray starts against the Nationals on Sunday. Neither Rizzo or Baker thought it fair to throw Stevenson into that fire. Wilmer Difo will start in left field instead, his first stint in the outfield since starting in center field a few weeks ago — which resulted in adventure and a late-game defensive replacement.

While Stevenson got a late call, Severino got a far earlier one, and arrived in Phoenix by 8 p.m. on Saturday night. The Nationals called up Severino to replace Raburn, a move Rizzo said was made as much out of convenience as roster need. Severino was already on the 40-man roster, and can serve as a late-inning pinch runner or right-handed bat. The Nationals did not want to add someone to the 40-man when Raburn seems likely to be gone just three days — though bereavement leave allows him to miss as many as seven.

Severino, who was the Nationals’ second catcher in last year’s National League Division Series, has struggled at Syracuse so far this season, plagued by injuries. He is hitting .211 overall, but is 4 for 15 with a homer in four games since returning from the disabled list last week.

“His numbers haven’t been there, but we feel that more recently he’s putting better at-bats together,” Rizzo said. “I think when he gets up here, he’s usually laser focused and prepared and I think he’ll give us a good solid at-bat. He always brings energy, he’s a good solid defensive catcher, could spell Matt a day or so and give him a little bit more rest. We’ve been working him pretty hard.”

So the Nationals’ roster, increasingly different from the one that began the season nearly four months ago now, gained two new faces again on Sunday morning, just before final game of a three-city road trip. Since the last time the Nationals were home, 20 percent of their roster has changed.

Sunday’s lineups:

Brian Goodwin CF
Wilmer Difo LF
Bryce Harper RF
Ryan Zimmerman 1B
Daniel Murphy 2B
Anthony Rendon 3B
Adrian Sanchez SS
Jose Lobaton C
Stephen Strasburg P

Daniel Descalso LF
Ketel Marte SS
David Peralta RF
Paul Goldschmidt 1B
Chris Owings SS
Chris Hermann C
Brandon Drury 2B
Gregor Blanco CF
Robbie Ray P

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