Phoenix, AZ -- (Sports Network) - Adam Dunn hit a two-run homer in his home debut and Conor Jackson chipped in two RBI, as Arizona held off San Diego for a 7-6 victory, in the opener of a three-game set.

Chris Snyder, Chris Burke and Mark Reynolds had an RBI each and Augie Ojeda had a pair of hits and as many runs scored for the D'Backs, who broke a tie atop the NL West and moved ahead of Los Angeles by one game. The Dodgers lost, 8-3, to Colorado on Tuesday. It was Arizona's fourth win in the last five games.

Doug Davis (5-7) was effective over six innings, surrendering two runs on seven hits while walking two and fanning six to get the win. Davis was winless over his previous three outings.

Adrian Gonzalez was 4-for-5 with two RBI and two runs scored while Chase Headley had two hits with an RBI and a run scored for San Diego, which has dropped five of its last seven games.

Josh Banks (3-6) struggled with his command from the outset in allowing six runs on four hits, while walking a season-high seven with three strikeouts in four frames.

"It just seems like his fastball command has alluded him and his secondary pitches have been a little erratic too," Padres manager Bud Black said. "I couldn't tell if it's something mechanics-wise or he is just trying to be too fine."

The Padres, trailing by four runs, made a game of it in the ninth off closer Brandon Lyon. Edgar Gonzalez led off with a double, Brian Giles walked two batters later and Kevin Kouzmanoff took a single to right to load the bases with one away. Adrian Gonzalez laced a two-run single to center and Headley stroked an RBI single to right, chasing Lyon from a 7-6 game.

"We put a nice finish on them," Black said. "Every hit in the ninth was big we just couldn't get that real big one at the end. All of our guys had good atbats in the ninth."

Tony Pena came on with runners on the corners, and got Nick Hundley to hit the ball back to the mound. Adrian Gonzalez was on third and broke for home, but was tagged out after getting caught in a rundown between third and home for the second out. Headley moved to third on the play, but Luis Rodriguez stranded him with a fly out to center, handing Pena his second save of the season.

"He (Pena) makes a great play on the groundball," D'Backs manager Bob Melvin said of the critical fielding play. "He is probably the one guy whether it is a bunt situation or anything in the infield you want on the mound. He is like having another infielder."

Arizona took a commanding 4-0 lead in the first off Banks. Ojeda and Chris Young started with walks before Jackson plated a run with an infield single. Dunn walked to load the bases for Reynolds, who lofted a sacrifice fly to right. Jackson and Dunn both advanced on an errant throw from right fielder Giles before Banks issued an intentional free pass to Chad Tracy to reload the bases. Snyder lined an RBI single to left and Burke capped the scoring with another sacrifice fly.

"It seems like since Adam (Dunn) has been here we have been a more patient club," Melvin remarked in reference to his club's big first inning. "He draws a lot of walks, hits a lot of home runs and since he has been here it seems like we have been a little more of a patient club and in that first inning and that's how it played out."

San Diego shaved two runs off its deficit in the second. Adrian Gonzalez and Headley started the inning with back-to-back singles and Hundley walked to load the bases. Tadahito Iguchi came through with an RBI single through the left side and Sean Kazmar followed with a sacrifice fly to right.

The D'Backs extended their lead in the fourth when Dunn clubbed his 33rd home run of the season, a two-run shot to right.

The two teams traded runs in the eighth. Pinch-hitter Jody Gerut hit an RBI single back through the middle off Jon Rauch in the top half, while Jackson plated a run with a single to center off Brian Falkenborg.

Game Notes:

Arizona leads the season series 8-5 and won 10 of 18 matchups from the Padres last season...The Padres made it official Tuesday, sending veteran pitcher Greg Maddux and cash considerations to the Los Angeles Dodgers for two minor leaguers to be named later or cash considerations...Wednesday's scheduled starters are Jake Peavy (9-8) for San Diego and Dan Haren (13-6) for Arizona...The Padres activated pitcher Brett Tomko off the 15-day disabled list Tuesday. He pitched 1 2/3 scoreless innings in relief of Banks.