Johnson pitched six solid innings and singled in a run, Dunn had a double in his Arizona debut and the Diamondbacks beat the Colorado Rockies 4-2 on Tuesday night.
"It felt good," Dunn said. "It's the first time I'd been a part of a win in a long time."
Dunn went 1-for-3 with two walks and Chad Tracy hit a home run for Arizona, which has won two straight after a four-game skid. The Diamondbacks acquired Dunn from the Cincinnati Reds on Monday for a minor leaguer and two players to be named.
"I didn't think I'd be as nervous as I was," Dunn said. "I swung at pitches I shouldn't have and took some pitches I probably should have swung at."
Diamondbacks manager Bob Melvin said he was happy with Dunn's first game.
"We expected Dunn to solidify the middle of the order and take some pressure off the other guys," Melvin said. "He did that and solidified the four hole in the lineup."
Johnson (10-8) allowed two runs and five hits, struck out seven and walked one to earn his sixth victory in his past seven starts. Chad Qualls and Jon Rauch pitched scoreless innings and Brandon Lyon pitched a perfect ninth for his 25th save in 30 chances.
"You could tell early on he was pretty good," Melvin said of Johnson. "He gave up the two, but after that he was pretty stingy."
Ubaldo Jimenez (8-11) lost his second successive start after winning six of his previous seven. He gave up 11 hits and four runs in six innings.
"Just enough mistakes across the board to put us down two runs at the end of the night," Rockies manager Clint Hurdle said.
"Usually you try to lay down on a bunt in that situation, but not when a guy is throwing 98 and has a pretty good curveball," Johnson said. "I took a swing thinking that anything can happen in this park and it did."
Jimenez said he was trying to get ahead in the count and left a pitch up in the zone.
"He just put the bat on it," he said. "It was away, but it was probably a little too high."
That was all Johnson and three relievers needed to all but end Colorado's chances of a second successive playoff appearance. The Rockies fell nine games behind NL-West leading Arizona.
"I got into a groove after they tied it," Johnson said. "My slider got better and the location of my fastball. The key was putting a zero up after we went ahead 4-2."
The Rockies had two runners on with one out in the fifth and seventh innings but couldn't cash in either time.
"Chances in the fifth and seventh innings we couldn't convert," Hurdle said. "We had a chance to win the game."
Tracy hit a two-run drive into the right-field bleachers in the second but the Rockies tied it in the bottom half. Iannetta led off with a home run to left, his 14th of the season. With two outs, Clint Barmes doubled down the left-field line and Ian Stewart doubled off the wall in right.
- MLB.com reported Tuesday that RHP Micah Owings will likely be one of the two players to be named in exchange for Dunn. Diamondbacks general manager Josh Byrnes declined to comment on the report.
- Rockies RHP Aaron Cook will miss his start Thursday due to lower back stiffness. Cook, who made his first All-Star Game this year, said he will throw on the side Thursday or Friday and a decision will be made then on the date of his next start.
- Rockies INF Garrett Atkins was scratched with strep throat.
- Arizona's Stephen Drew extended his hitting streak to 14 games.