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WASHINGTON -- Tim Stauffer was back on the mound for the San Diego Padres and feeling good after missing more than five weeks with a strained right elbow.

The results, however, were not quite what he wanted.

Activated from the disabled list before the game, Stauffer gave up Bryce Harper's first major league home run in a spotty five innings of work as the Washington National beat San Diego 8-5 Monday night.

"I wish it had gone a little differently, a little better," Stauffer said. "Obviously you'd like to have a few back, but all and all it was just good to get out there again."

Yonder Alonso and Chase Headley each had a double and a single for San Diego, which lost its second in a row and fourth in five games.

The Padres' opening-day starter last season, Stauffer gave up four runs -- three earned -- on seven hits. He struck out five and walked three.

"Stauf battled, he really did," Padres manager Bud Black said. "I didn't see any ill effects from the elbow situation."

Stauffer didn't allow a hit over the first two innings, although the Nationals scored a run in the first when Ian Desmond reached on a two-base error by Headley and later scored on Adam LaRoche's groundout.

In the third, Stauffer ran into trouble as the Nationals scored three runs.

Ryan Zimmerman had a run-scoring single and Roger Bernadina scored from third when Headley missed a pick-off throw from catcher Nick Hundley. Then the 19-year-old Harper drove a two-out, 2-1 pitch to the grass backdrop in center field, just to the left of the 402-foot marker.

"I had fallen behind a little bit," Stauffer said. "The pitch that he hit out was supposed to be a backdoor slider and it just caught a little more plate than I would have liked. Really not a terrible pitch, it was down and just over the plate in a spot where a lefty can do some damage."

Harper raced around the bases quickly and continued his sprint straight to the dugout, where he exchanged high-fives with teammates. As the crowd cheered, Harper came to the top of the dugout steps for a curtain call, thrusting his right index finger into the air.

He's 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.

Harper's homer gave the Nationals a 4-1 lead, but San Diego tied the game with a three-run inning in the fourth. With two on and one out, Orlando Hudson hit a single to center field that scored two runs.

Alonso scored first, then Headley bowled into Sandy Leon on a play at the plate, causing the catcher's right ankle to buckle under him. Leon rose and limped a few steps before dropping to his knees and then was helped off the field. Leon left the game with a high right ankle sprain.

"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."

Stauffer scored Hudson on a sacrifice bunt with two outs to tie the game. An inning later, Headley gave the Padres a 5-4 lead with a run-scoring single.

Mile Mikolas (0-1) came on in the sixth and allowed two runs on two hits while getting just one out. Desmond put Washington ahead for good in the sixth with a two-run double off the right field wall.

Craig Stammen (3-0) pitched two innings for the win. Chad Tracy and Xavier Nady added a pair of insurance runs for the Nationals with eighth-inning solo homers off reliever Luke Gregerson.

The Padres were in position to rally in the ninth when Washington 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.

"You hate losing games when you swing the bats well enough, especially the way we are, a team that usually relies more on pitching and defense to carry us," Headley said. "When you put up the runs you feel like you have a pretty good chance to win."

Game notes

San Diego OF Jeremy Hermida is scheduled to undergo sports hernia surgery on Tuesday and will be out up to six weeks, Black said. Hermida has been on the DL since late April.