WASHINGTON -- Whether he's launching home runs, nicking foul balls or striking out, Adam Dunn tries to keep it simple at the plate -- look for a pitch to hit, and hit it hard.
"I don't have an approach to change," Dunn said. "That's all I've got."
Dunn hit a three-run shot in the first inning, added a solo homer in the third and capped his power show with a leadoff drive in the eighth that landed in the seats above the out-of-town scoreboard in right-center field. The crowd of 13,762 showed its appreciation, making enough noise to bring Dunn out to the top step of the dugout for a curtain call. Dunn left the game in the ninth for a defensive replacement.
"It's pretty cool to hit three homers, but the last one, since we won, was obviously the biggest," Dunn said. "I don't feel any different than I have in the past. I got pitches to hit tonight and didn't foul them off like I've been doing."
Dunn became the second player with a three-homer game for the Nationals. Alfonso Soriano did it in 2006. This was the first three-homer performance in the three-season history of Nationals Park.
Dunn reached the 20-homer mark for the 10th straight season. He has 336 career home runs.
"That's what he can do," said third baseman Ryan Zimmerman, who had a RBI single in Washington's four-run first inning. "He's one of the best, if not the best, power guys in the game for the last five, six years. It's good to have him on your team."
Dunn's third homer came after the Padres had scored twice in the top of the eighth to close to 6-5, and San Diego rallied again in the ninth.
Matt Stairs hit a solo homer in the ninth off Nationals closer Matt Capps -- his 20th career pinch-hit home run, tying the major league record set by Cliff Johnson. The Padres then put runners on the corners before Capps got Chase Headley to ground out for his 23rd save in 27 chances.
Nationals manager Jim Riggleman said he's not worried when his closer gets into a jam.
"If we've got a three-run lead he might give up one or two, if we've got a one-run lead he generally puts a zero up there," Riggleman said. "He's right there at the top of the lead in saves, and that speaks for itself."
Ian Desmond also hit a solo home run for the Nationals, who earned a series win against the Padres for only the second time in 12 tries since moving to Washington in 2005.
Adrian Gonzalez homered, doubled and singled twice for the Padres and drove in two runs.
J.D. Martin (1-4) got his first win since Sept. 18, 2009. He gave up two runs on six hits, walking one and striking out four in 5 2/3 innings. Martin's win came despite struggles with his curveball, his best pitch.
"Tonight it wasn't tempting enough to get too many guys to swing at it," Riggleman said.
Martin had gotten little run support -- in his previous six starts, the Nationals scored a total of 12 runs while he was in the game -- but the Washington hitters gave him an early cushion against San Diego.
Washington's first five batters reached base, and the Nationals scored four runs, on Zimmerman's single and Dunn's homer to center, before Jon Garland recorded an out.
"I've been getting killed in one inning," Garland said. "In one inning, I've got to cut it down. Because of that I haven't been giving us a chance to win ballgames."
Garland (8-6) settled down and pitched six innings, giving up six runs on eight hits, including a season-high three home runs.
Gonzalez drove in the Padres' first two runs, with a solo home run in the first inning, his 17th of the year, and an RBI double in the third.
Dunn answered in the bottom of the third, leading off with his drive that landed just a few seats away from his first shot.
"He's a prolific home run hitter. That's what he does," Padres manger Bud Black said. "You make a mistake, and at times he'll make you pay."
Padres RHP Chris Young, who has been on the DL since April 7 (right shoulder strain), played catch before the game and then returned to San Diego for the expected birth of his second child. ... Dunn has 26 multihomer games in his career. ... The game-time temperature of 98 was the second-highest in Nationals history. Tuesday's temperature was 99 degrees.