Dunn led off the second inning with his 31st homer and Washington pounded the Cincinnati Reds 10-6 after struggling to score in its previous four games.
Washington scored six times in the third and added three more in the fourth after totaling five runs in the previous four games, three of them losses.
"We went through three or four days where we didn't get many runs," manager Jim Riggleman said. "In both of those rallies tonight, we hit some balls down the line that stayed fair. They turned into six RBI."
J.D. Martin (2-2) cruised to his second consecutive win in his sixth career start, allowing an unearned run and six hits over six innings. The rookie right-hander was 0-2 with a 7.16 ERA before he pitched five solid innings against Arizona last Sunday.
"The run support was awesome," Martin said. "I felt like I was throwing strikes. I kept telling myself to keep throwing strikes. I got a little lucky with two batters called out trying to bunt. I'll take any help I can get."
Cueto fell to 0-6 with a 10.64 ERA in his last eight starts as the Reds lost for the third time in four games. Cueto hasn't won since beating Arizona 1-0 on July 1, but manager Dusty Baker wasn't concerned that the right-hander's workload -- which included pitching in winter ball and the World Baseball Classic -- was catching up with him.
"He's throwing the ball good," Baker said. "His velocity was good. It's a matter of location. They cheap-hitted him to death. Their cheap bloopers led to big innings."
"My arm's fine," Cueto said through an interpreter. "I don't feel any pain. It just feels like the ball isn't coming out of my hand good. I don't think it's anything mechanical. I just wasn't aggressive to the hitter."
Dunn, known for his tape-measure shots to right field, started the second with a drive that barely reached the first row of seats in left field. It was his 125th homer at Great American Ball Park -- the most by any player.
Dunn made his major league debut with Cincinnati in 2001 and was one of the club's regular outfielders until he was traded to Arizona last August. He signed with Washington in the offseason.
The Nationals scored six times in the third, sending 10 batters to the plate. Martin started the inning with a single to left and ended it by striking out. Rafael Belliard had a run-scoring double and Ryan Zimmerman and Josh Willingham added RBI singles before Gonzalez cleared the bases with a three-run double into the left-field corner on an 0-2 pitch with two outs.
"That's what hurt us," Baker said.
Cueto (8-10) allowed seven runs and eight hits in 2 2/3 innings.
Sutton went deep in Cincinnati's four-run seventh, hitting a two-run shot into the visitors' bullpen in right.
Martin committed two throwing errors. ... Baker said RHP Homer Bailey should be ready to make his next scheduled start Tuesday against San Francisco. Bailey left his last start Wednesday at St. Louis when Albert Pujols lined a ball off the pitcher's left foot. ... Reds hitting coach Brook Jacoby was ejected by plate umpire Greg Gibson in the bottom of the second after complaining about the second Reds batter in two innings being called out for getting hit by a bunted ball in fair territory.