Phoenix, AZ -- (Sports Network) - Adam Dunn hit a three-run homer and walked twice, as the Arizona Diamondbacks held on for an 8-6 win over San Diego, in the second of three games with the Padres.

The game was expected to be a pitchers' battle between Arizona's Dan Haren, who came into the game with a 2.96 earned run average, and San Diego ace Jake Peavy, who won the 2007 NL Cy Young Award and carried a 2.61 ERA into the contest.

Instead, Haren (14-6) got enough run support to take the win, after allowing five runs on 11 hits in six innings. Peavy (9-9) took the loss after surrendering six runs -- five earned -- on five hits and four walks in five frames.

"We were thinking the same thing," Arizona manager Bob Melvin said. "You don't see seven runs scored off of Haren and Peavy too often in the first inning...Both guys didn't have their best stuff today."

Conor Jackson and Mark Reynolds each finished with a hit and two runs batted in for the Diamondbacks, who have won both games of the series so far and five of six overall. Arizona took a two-game lead over Los Angeles for first place in the NL West, after the Dodgers lost to Colorado on Wednesday.

Jody Gerut went 3-for-5 with a solo homer, and Kevin Kouzmanoff hit a two-run blast for the Padres, who have lost three in a row.

San Diego did most of its damage in the first inning. Gerut and Tadahito Iguchi led off with back-to-back doubles to plate one run, and two batters later, Adrian Gonzalez singled home Iguchi. Kouzmanoff followed with a two-run shot to left field to give San Diego a 4-0 lead.

But the Diamondbacks responded in the home half. With one out, Augie Ojeda doubled, and Jackson followed with a walk. That brought up Dunn, who hit his National League-best 34th home run of the season to bring the D-Backs within one.

"I know he didn't want to load the bases and I kind of guessed right and I got a fastball," Dunn said. "Put a good swing on it and that's what happens."

Arizona surged ahead in the second. With one out, Chris Snyder launched a solo homer to left field to tie the game. Haren then worked a walk and Stephen Drew singled -- both runners advanced because of right fielder Brian Giles' fielding error. After Ojeda popped out, Jackson smacked a two-run single to right for a 6-4 lead.

"Obviously it's disappointing," Peavy said. "We come out against a guy like Dan Haren, who's been as good as anybody all year, score four before I take the field...it's unacceptable when you can't hold that lead. (I) competed tonight but just didn't have it."

The game stayed that way until the sixth inning, when the Padres trimmed one run off its deficit. Nick Hundley stroked a one-out double and advanced to third on a ground out, then scored when pinch-hitter Brian Myrow singled. Haren, though, rebounded to get Gerut to line out and end the inning.

The Diamondbacks plated a pair of insurance runs in the seventh.

Ojeda led off with a walk facing Clay Hensley, who came on for Peavy in the sixth. Hensley got Jackson to fly out, but was then lifted for Wilfredo Ledezma. However, the new Padres pitcher walked Dunn and pinch-hitter Tony Clark to fill the bases. Reynolds hit a two-run double to left to provide an 8-5 lead for Arizona.

After Tony Pena tossed a scoreless eighth for Arizona, Jon Rauch entered for the ninth and got the first two outs before giving up a solo homer to Gerut. However, Rauch got Iguchi to ground out, ending the game.

Game Notes

Kouzmanoff's homer was his 19th of the season, a new career high. He hit 18 last season for the Padres...Rauch notched his 18th save of the season...No Diamondbacks player had more than one hit, and the club had fewer hits (six) than runs.