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WASHINGTON -- Bryce Harper is as sentimental about his first big league homer as he is about the rest of the many milestones in his baseball career.

The ball's headed for a cardboard box.

The 19-year-old rookie became the youngest major leaguer to homer since 1998 with a solo shot in the third inning of the Washington Nationals' 8-5 victory over the San Diego Padres on Monday night.

After the game, the ball was sitting in his locker with "1st ML HR" written on it in ballpoint pen. The keepsake was going to get a place alongside his first home run ever -- at around age 7 -- and other mementos. He had a hard time remembering other saved items.

"I don't really keep track," Harper said. "All my stuff is in just a box. Posters, magazines -- I don't really care."

Harper raced around the bases quickly after driving a 2-1 pitch from Tim Stauffer onto the grass backdrop just to the left of the 402-foot marker in the third inning. He continued his sprint straight to the dugout, where he exchanged high-fives with teammates.

Harper is the youngest player in the majors -- and, at 19 years, 211 days old, the youngest to hit a homer since Adrian Beltre of the Los Angeles Dodgers connected when he was 19 years, 171 days old on Sept. 25, 1998, according to STATS LLC.

The home run came in the outfielder's 15th game and 54th at-bat with the Nationals.

The crowd at Nationals Park cheered until Harper came to the top of the dugout steps for a curtain call, thrusting his right index finger into the air.

"It was pretty cool. I was pretty excited about that," Harper said. "I wasn't sure if I should've went up there, but all the veteran guys were like, 'Go. Get up there.' "

Harper's homer, along with solo shots by Chad Tracy and Xavier Nady in the eighth inning, lifted Washington to the victory but the Nationals also suffered another in a long line of injuries this season.

Catcher Sandy Leon -- making his major league debut -- left the game in the fourth inning after suffering a high right ankle sprain in a collision at home plate. Chase Headley was one of three Padres to score in the fourth when he bowled into Leon on a play at the plate, causing the catcher's right ankle to buckle under him.

"I don't know if it was the throw that kind of took him in there, but he really left me nowhere to go," Headly said. "It's really unfortunate that it happened."

Nationals manager Davey Johnson said Leon would go on the disabled list and the team would likely call up catcher Carlos Maldonado from Triple-A Syracuse.

Leon had his right leg in a tall boot-like brace in the clubhouse after the game and did not speak with reporters. He was called up from Double-A Harrisburg on Sunday to replace catcher Wilson Ramos, who tore the anterior cruciate ligament in his right knee a day earlier at Cincinnati. Leon started Monday's game and struck out in his only at-bat.

"It's tough seeing Ramos go down the other night, then when Sandy gets here -- you hate seeing a guy go down, let alone in his big league debut," said Nationals starter Ross Detwiler, who gave up a season-high four earned runs in five innings.

The Nationals led 8-6 going into the ninth inning. Closer Henry Rodriguez walked the bases loaded with one out before giving way to Sean Burnett, who got Jesus Guzman to ground into a 1-2-3 double play for his first save.

"If you can draw it up, that's probably the play," Burnett said.

Craig Stammen (3-0) pitched two innings for the win. Miles Mikolas (0-1) gave up two runs and two hits while getting just one out.

Headley was in the middle of several of the game's big moments. He doubled in the fourth before scoring on the play that knocked out Leon and briefly gave the Padres a 5-4 lead an inning later with an RBI single. He also made two errors.

Stauffer was reinstated from the disabled list before the game and started for the first time this season after being sidelined with a strained right elbow. He gave up four runs -- three earned -- on seven hits in five innings. He struck out five and walked three.

Harper's homer gave the Nationals a 4-1 lead, but San Diego tied the game with a three-run inning in the fourth, including Orlando Hudson's single to center field that scored two runs, the second coming on Headley's collision with Leon.

After Headley gave the Padres the lead an inning later, Ian Desmond put Washington ahead for good in the sixth with a two-run double off the right field wall. Nady and Tracy added a pair of insurance runs with their eighth-inning solo shots.

Game notes

Washington manager Davey Johnson said before the game Rodriguez would remain the team's closer, despite Rodriguez blowing his third save in 11 chances Sunday against the Reds. After the game, Johnson reiterated that he still has confidence in his closer despite another shaky outing. ... In a rehab start at Triple-A Syracuse on Monday, RHP Chien-Ming Wang threw eight-plus innings, allowing four earned runs and 11 hits with one walk, one strikeout and one hit batter. ... Johnson said OF Michael Morse is on pace to return when interleague play begins June 8 at Boston. ... The Padres optioned LHP Josh Spence to Triple-A Tucson before the game. ... San Diego OF Jeremy Hermida is scheduled to undergo sports hernia surgery on Tuesday and will be out up to six weeks, manager Bud Black said. Hermida has been on the DL since late April.