Phoenix, AZ (Best E Casino) - Adam Dunn hit the go-ahead, two-run home run in the eighth inning and the Arizona Diamondbacks kept pace in the NL West standings with a 3-1 win over the San Francisco Giants in the opener of a four-game series from Chase Field.

Starter Doug Davis tossed seven innings and gave up just one unearned run on eight hits without walking a batter and Tony Pena (2-2) received the win with a perfect eighth. Chad Qualls came on in the ninth to earn his fourth save of the season for the D'Backs, who snapped a two-game skid to keep from falling further back of Los Angeles in the division. Justin Upton hit a solo blast to account for Arizona's other run.

The Dodgers have won 13 of 15 overall to pull 4 1/2 games ahead of Arizona for the division lead while Arizona has lost eight of its last 10 games.

"We knew early on that they (LA) had won, it puts a little more pressure on you, and maybe it makes you focus a little more, I don't know, we are not in a position right now where we're playing great," Arizona skipper Bob Melvin said of the NL West race with the Dodgers. "They are playing great. You go out there and look at the scoreboard and it means a lot. I think we just have to start playing better, first, before we get too fixated on the scoreboard."

Brad Hennessey (1-2) went the distance but allowed the two home runs among the D'Backs' eight hits and took the loss. The right-hander struck out two and did not walk a batter in the eight-inning decision. San Francisco was coming off wins in its last three contests and is 9-3 over its past 12 contests.

"I thought it was a great effort, he (Hennessey) pitched a great game," Giants manager Bruce Bochy said. "One run going into the eighth in this ballpark, he did a terrific job, we just didn't get a key hit there. We had some opportunities, but just couldn't get it done tonight"

Chris Young started the eighth with a single and, after David Eckstein failed on a sacrifice attempt and Upton lined out, Dunn stepped to the plate and turned on Hennessey's first-pitch fastball. The ball travelled over the fence in right field for a 3-1 lead. Qualls set the Giants down in order in the ninth to make the lead hold up.

"I think every game from now on is very important, we had a chance to separate ourselves and we didn't do that," Dunn said of the stretch run. "That's all in the past now, all we can do is look forward, play as good as we can and win as many games as we can. The Dodgers are going to have to help us out."

Rich Aurilia ripped a single back through the middle with two away in the third and came home when Young misplayed a ball in center off the bat of Bengie Molina.

Upton erased the run one inning later with a leadoff homer to deep center field to tie the game 1-1.

Game Notes

Arizona now leads the season series 8-7...Tuesday's scheduled starters are Matt Cain (8-12) for the Giants and Dan Haren (14-8) for the D'Backs...Arizona was 1-for-4 with runners in scoring position and are just three for its last 39 over the last four games in that category...Dunn's home run was his 37th of the season, good for second-best in the Majors...The D'Backs are 6-16 in their last 22 games...Arizona's Josh Whitesell got his first major league hit, a single in the seventh.