"The year hasn't gone the way I've wanted to," Reynolds said. "Maybe tonight will jump start me into a nice little run down the stretch."
Reynolds acknowledged being slightly gun shy after getting hit in the head by a pitch three weeks ago, leading to lackluster results at the plate.
"I've been pulling off a lot of pitches," he said. "When you get hit in the head it's tough sometimes to stand in there against the heater. I'm just trying to be consistent."
Pablo Sandoval homered for the Giants, who have lost three straight to fall 1½ games behind Philadelphia in the wild-card chase.
Hudson (4-1) gave up two runs, walked two and struck out six. He has pitched at least seven innings in each of his six starts since the Diamondbacks acquired him from the White Sox last month.
"It was kind of tough to stay warm with all the long innings," Hudson said. "I like getting the runs but when the tempo picked up I was able to get into a groove."
Zito (8-10) allowed a season-high nine runs over 3 2/3 innings. He yielded six hits, walked five and struck out one. The 2002 AL Cy Young Award winner has lost his last six decisions.
"The pitches just aren't crisp right now," said Zito, who has allowed 13 runs in his last 8 1/3 innings. "It requires working hard between starts. It's a matter of getting the feel out there. I just have to do better."
San Francisco's pitching staff has surrendered 29 runs over the past three games, and manager Bruce Bochy met with his starters after the Giants' latest loss.
"This isn't going to work," Bochy said. "We're not getting it done and the starting staff is what we're built on. We're going to have to get it fixed pretty quick. It's getting away from us early."
Two-time reigning NL Cy Young Award winner Tim Lincecum allowed three runs in the first in Arizona's 6-0 victory Friday night, snapping a seven-game losing streak to the Giants. And the Diamondbacks were even more successful in the opening inning of the second game of the series.
"We're pitching ourselves into jams," Bochy said. "We need to be more aggressive with our pitchers. They all need to step up."
LaRoche drove in Arizona's first run with a groundout and Montero cleared the bases with a double. Jose Guillen dropped Stephen Drew's fly ball to right, allowing two more runs to score.
"The ball was going sideways by the time it came down to Guillen," Arizona manager Kirk Gibson said. "We got a couple of free ones there and we'll take them."
Reynolds, a .500 hitter (8 for 16) for his career against Zito, hit his 29th homer in the fourth.
In the ninth, LaRoche, who has 21 RBI in 26 games in August, launched a towering shot into McCovey Cove, recording the 22nd splash hit by an opponent at AT&T Park and his second in two nights.
- Giants C Buster Posey was held out after injuring his left forearm Friday. He's expected back on Sunday.
- Giants RHP Brian Wilson was hit in the side of his neck when he missed a toss from Santiago Casilla while playing catch before the game.
- Arizona RHP Brandon Webb threw a 52-pitch simulated game and felt good about the outing.
- Arizona 3B coach Joel Youngblood turned 59 Saturday.