Dunn hit his National League-leading 34th home run, his second in as many games, and the Arizona Diamondbacks beat the San Diego Padres 8-6 on Wednesday night.
"After giving up a four-spot with Peavy on the mound you look down and start seeing what bullpen guys can get you through the game," said Arizona manager Bob Melvin. "And then suddenly it's 4-3."
The three runs were courtesy of Dunn, who followed a double by Augie Ojeda and a walk to Conor Jackson with a scorching line drive just over the right-field fence for his second home run in as many days.
"I knew he didn't want to load the bases and I kinda guessed right," said Dunn, who played his second home game at Chase Field since he was traded to the Diamondbacks from Cincinnati on August 11. "You don't really expect to score a lot of runs against one of the game's best pitchers."
Chris Snyder also homered for the Diamondbacks, who have won five of seven to maintain their lead over Los Angeles in the NL West.
Haren (14-6) struggled through a six-inning stint but won for the seventh time in eight outings.
Haren surrendered five runs and a season-worst 11 hits with four strikeouts. Haren did not walk a batter for the eighth time in 26 starts.
"I obviously didn't have good stuff today but I battled and tried to give the guys a chance to come back," Haren said. "Giving up four in the first to him [Peavy], obviously I didn't like my chances."
Fortunately for Haren and the Diamondbacks, Peavy also was nowhere close to top form.
Peavy (9-9) allowed a season-high six runs -- five earned -- and five hits over five innings with four walks and two strikeouts for his third loss in his last four starts.
"Four walks, that's not Jake's game," said Padres manager Bud Black. "He's usually in and around the plate, especially when he has the lead. That wasn't typical Jake."
San Diego needed five batters to take a 4-0 lead against Haren in the first. Jody Gerut and Tadahito Iguchi hit consecutive doubles to lead off the game, Adrian Gonzalez hit a one-out RBI single and Kouzmanoff hit his 19th home run into the left-field bullpen.
But the defending Cy Young Award winner couldn't hold the lead. Dunn pulled the Diamondbacks within 4-3 and Snyder tied the game in the bottom of the second with a one-out homer to left.
Peavy walked Haren, Stephen Drew singled to right and Conor Jackson hit a two-run single to right to give the Diamondbacks a 6-3 lead after sending just 12 batters to the plate.
"It's unacceptable when you can't hold that lead," Peavy said. "I just didn't have it. I couldn't throw the ball where I wanted to throw it. I just didn't make pitches. That's all there is to it."
Peavy's outing was his shortest since a four-inning start May 14 at Chicago Cubs, one day before he was placed retroactively on the 15-day disabled list with a right elbow strain.
Melvin said Lyon, who allowed three runs in a non-save situation on Tuesday, was given a regular day off. "He will close tomorrow," Melvin said. ... Snyder has hit three home runs in the last seven days. ... Dunn drew his major league-leading 90th and 91st walks in the fifth and seventh innings. ... Haren has lasted six or less innings in three of his last four starts. ... San Diego has a major-league high 31 home runs on the road since the All-Star break. ... Peavy has pitched five or fewer innings in nine of 25 career starts against Arizona. Peavy is 11-11 with a 4.88 ERA against the Diamondbacks. ... Brian Giles moved within two hits of Ryan Klesko for seventh on the Padres' career list with 787. ... Gerut is 5-for-8 with a double and a homer in his career against Haren.