Bryce Harper, 19, will become the youngest player in the majors when he makes his debut Saturday against the Dodgers. (Toni L. Sandys/THE WASHINGTON POST)

The Washington Nationals recalled Bryce Harper from Class AAA Syracuse on Friday after placing third baseman Ryan Zimmerman on the 15-day disabled list with right shoulder inflammation, promoting the first overall pick of the 2010 draft to the majors five months before his 20th birthday.

Harper will make his major league debut Saturday at Dodger Stadium, a call-up that came faster than Harper or the Nationals anticipated and necessitated by injuries.

General Manager Mike Rizzo made his bones in player development, and he crafted a careful scheme for Harper’s ascension, which included 250 to 300 at-bats at Class AAA Syracuse. But with left fielder Michael Morse out until midseason, Zimmerman also sidelined and punchless bats currently occupying left field, Rizzo traveled to Rochester, N.Y., this week to personally scout Harper. After watching him play left field for three days, Rizzo decided Harper — 72 at-bats into his Class AAA career — would come to the majors, ready or not.

“The decision is really a team decision,” Rizzo said. “It’s to support the major league club when we need an offensive player to play corner outfield. . . . This wasn’t the coming-out party for Bryce that we had in mind. This wasn’t the development plan we had in mind.”

Harper will bat seventh Saturday and play left field behind starting pitcher Stephen Strasburg, the 2009 first overall pick who has blossomed, at 23, into the Nationals’ ace. Will Harper play every day?

“Yes,” Manager Davey Johnson said. “As far as I’m concerned, he’s earned the right to have the opportunity. He fits what we’re looking for. A good player coming up to the big leagues is the way I look at it.”

The Nationals made the final decision Friday afternoon, after Zimmerman visited a doctor in Los Angeles who confirmed that the third baseman needed to rest the inflamed AC joint in his right shoulder. The Nationals expect Zimmerman to return May 6, the first day he is eligible to come off the disabled list.

Rizzo followed the usual protocol for informing a first-time big leaguer he had made it. He told Director of Player Development Doug Harris, who relayed the news to Syracuse Manager Tony Beasley. Beasley called Harper into his office and told him he would become the youngest player in the major leagues.

“He didn’t say a lot,” Beasley said in a telephone conversation. “I think he was kind of speechless. We just talked a little bit. Gave him some advice. He was just kind of taking it all in. He was very grateful and humble at the same time. It’s a big day for the whole organization.

“I don’t think he anticipated it,” Beasley added. “None of us did at this point. This is something he’s wanted to achieve for basically his whole life.”

Rizzo left the decision of how much Harper will play to Johnson, who advocated for Harper to make the major league roster out of spring training. But “we didn’t bring Bryce up there to sit on the bench,” Rizzo said.

The move to call up Harper now represents a shift for the Nationals, who started the season 14-5. When they wallowed at the bottom of the standings, they focused on development first and only. Winning has now taken precedence, even when it comes to Harper.

“He does too many things that can help us win games,” Zimmerman said. “That’s the goal up here now. Two or three years ago, it was, let’s prepare these kids and make sure they’re ready to play whenever we get good. Well, whenever we get good is now.”

The Nationals will monitor Harper’s progress in the major leagues before deciding if he will stay for good or potentially return to Syracuse. Rizzo mentioned Los Angeles Angels prospect Mike Trout as a possible template — the Angels promoted him last year out of need, but after Trout struggled they sent him back to Class AAA. This year, Trout has become one of the most talented minor leaguers in the sport, and he too was called up later Friday evening.

“With Bryce’s makeup and his attitude and his confidence level, I don’t have many reservations,” Rizzo said. “I expect him to play well. I know this guy is a very confident person. If it doesn’t, he’s not the type of guy it’s going to derail his development plan whatsoever.

“I’m also reserved to the possibility that this may not be his breakout moment. Like Trout with the Angels, there could be a step sideways to take a leap forward.”

Teammates agree Harper is confident, even brash. But the attitude, they said, will only help him weather the media storm sure to accompany his arrival.

“He’s very confident,” Zimmerman said. “Everyone in this room is confident, or we wouldn’t be here. Bryce, not so much anymore, but at first, had a different way of expressing his confidence. I said at first. From last spring training to this spring training, I’ve never seen somebody grow up as quickly as he has in one year. The way he carries himself, he thinks things differently now.”

At Syracuse, Harper has hit .250 with a .333 on-base percentage and a .375 slugging percentage. He heated up lately, going 5 for 13 with his lone home run during his past five games. He was “toning himself down at the plate, just relaxing a little more,” Beasley said.

“We had a development plan in mind,” Rizzo said. “We still have a plan. If we didn’t think he could perform in the major leagues and not hurt his developmental plan, we wouldn’t make the move.”

Johnson would not even contemplate the notion of Harper returning to the minors. He did not want to look ahead, and he does not want to think in negative terms.

“He’s been swinging the bat good, and he fits the bill in organization to come up,” Johnson said. “And he’s going to play. Enough said.”

The biggest challenge for Harper may be hitting left-handed pitching. At Syracuse, Harper hit 4 for 21 with six strikeouts against lefties. But both Rizzo and Beasley said Harper has made strides against southpaws, Rizzo calling his approach “fearless.”

“His numbers against lefties are probably not as good as the at-bats that he’s had,” Beasley said. “He competed well.”

The Nationals waited long enough before promoting Harper to ensure they will maintain his rights for six full seasons beginning in 2013 before he becomes eligible for free agency.

When Beasley called Harper into his office Friday, he was calmer than Beasley expected. Harper has been playing with older competition his whole life, and, as one Nationals coach said, “he always found a way to be the best player on the field.”

Now, he will try to be the best player on the biggest of fields.

“He was obviously excited about it,” Beasley said. “Probably a little nervous at the same time.”

Nationals note: Co-closer Brad Lidge was placed on the 15-day disabled list with an abdominal strain, which will make Henry Rodriguez the Nationals’ full-time closer. Reliever Ryan Perry was called up from Syracuse and was scheduled to join the team Friday night in Los Angeles to replace Lidge in the bullpen.

Lidge, who has not thrown since last Saturday will travel to Philadelphia on Monday to see a specialist for further testing.