PHOENIX -- Adam Dunn was happy to be back in Arizona.
The crowd at Chase Field was announced at 15,670. Arizona started playing in the National League in 1998.
Dunn, who played 44 games for Arizona in 2008, hit a two-run shot in the first inning. He hit his 28th home run in the fourth, a solo drive. He added an RBI single in the seventh.
"Honestly, I didn't like hitting here before I got traded over here," Dunn said. "I think it's one of those things where the more you play in a ballpark, the more familiar you get with it, and now I feel really comfortable with it."
Adam Kennedy drove in a pair of runs with a single in the third and a seventh-inning double in support of Craig Stammen (4-4).
"He had me on the top step [of the dugout] a couple of times. There was two runners on just about every inning," Nationals manager Jim Riggleman said of Stammen. "That's a tough way to pitch."
Ian Kennedy (6-9) struck out the first two batters of the game, then gave up a double to Ryan Zimmerman and Dunn's first home run.
Mike Morse hit a solo home run in the eighth for the Nationals. Adam LaRoche hit his 17th home run in the eighth for Arizona.
Mark Reynolds returned to the Arizona lineup after being hit in the helmet by a pitch and leaving Tuesday night's game. But after striking out three times, he was replaced at third base in the seventh inning for precautionary measures when he said he wasn't feeling well.
"I looked at him and it was obvious something was wrong," Diamondbacks manager Kirk Gibson said. "He was just struggling. It has something to do with him being hit last night and we had to get him out of there for sure."
New Diamondbacks outfielder Ryan Church, acquired from Pittsburgh in a trade July 31, doubled in the second inning in his first at-bat with his new team.
The Diamondbacks scored in the first on a leadoff walk to Chris Young, Kelly Johnson's single and a sacrifice fly by Justin Upton. But Stammen scattered five more hits over a total of 5 1/3 innings.
The Diamondbacks optioned infielder Tony Abreu, who had been with the major league club all season, to Triple-A Reno and called up reliever Rafael Rodriguez. General manager Jerry DiPoto said the team wanted to get more at-bats for Abreu, who had 131 in 60 games. ... Arizona pitcher Juan Gutierrez, placed on the 15-day disabled list Tuesday with right shoulder inflammation, will be shut down for four or five days before throwing again, DiPoto said. ... Nationals OF Nyjer Morgan got Wednesday off because of a nagging hip injury, but was available to pinch-hit. He said before the game he felt a sharp pain in his hip when jogging.