PHOENIX -- Kicking off an important homestand, the NL West-leading Arizona Diamondbacks wanted to be aggressive early, hopefully put some pressure on San Diego to keep their momentum going.

Arizona did just that -- got some plenty of help from the Padres, too.

Josh Collmenter pitched effectively into the sixth inning and the Diamondbacks took advantage of San Diego's shaky defense to beat the Padres 5-0 on Friday night.

"We came out very aggressive, we stole four bags on them, and kind of forced some action," Diamondbacks manager Kirk Gibson said. "We'll take it like that when it's available. We'll take runs any way we can get them."

Arizona put pressure on San Diego early with aggressive baserunning and the Padres had no answer, fumbling and bumbling their way to three errors in the first two innings.

Collmenter (8-8) had his fourth straight solid outing, allowing six singles in 5 1/3 innings, and combined with four relievers for Arizona's second shutout during a four-game winning streak that has the Diamondbacks three games ahead of San Francisco in the division.

"Anytime you can get a few runs before you go out for the second is huge," Collmenter said. "A lot of times, one run can make the difference, help your confidence."

The Diamondbacks, with San Diego's help, gave Collmenter a nice cushion, scoring all of their runs off San Diego starter Wade LeBlanc (2-3) in the first two innings. The Padres never fully recovered, holding Arizona without a run the rest of the way, but going 0-for-6 with runners in scoring position.

"I don't know if I ever have seen and inning go like that first inning," LeBlanc said. "Obviously, it put us in a big hole. There wasn't a whole lot hit hard in that first inning, but they put them where they needed to put them."

Arizona had surged to the top of the NL West, only to slide back with a six-game losing streak.

In danger of spiraling downward, the Diamondbacks recovered to make it a respectable road trip, closing it out with three straight wins over Washington for their first division lead this late in the season for the first time since 2008.

Heading home for a crucial six-game homestand against NL West opponents, the Diamondbacks hoped to keep it going behind Collmenter.

The over-the-the-top-throwing rookie did his part, retiring the first eight batters he faced while allowing less than two runs for the fourth straight start.

The Diamondbacks -- with plenty of help from San Diego -- made sure Collmenter didn't have to work too hard, scoring four runs in the first.

Arizona had five hits in the opening inning and Padres catcher Nick Hundley sent two runs across the plate with throwing errors -- the first coming when he hit Ryan Roberts' swinging bat while trying to throw out Willie Bloomquist as he attempted to steal third.

Right fielder Will Venable also had a not-so-graceful belly flop attempting to catch Paul Goldschmidt's pop-up down the line and left fielder Kyle Blanks went down awkwardly on Aaron Hill's double, adding to the ugliness.

It continued in the second inning, when first baseman Jesus Guzman dropped a throw by Logan Forsythe to allow another run, making it 5-0.

Those early problems helped wear out LeBlanc, who threw 91 pitches in four innings while allowing five runs -- four, somehow, were earned -- on seven hits. In his fifth stint with the Padres this season, LeBlanc hadn't allowed more than three runs in seven previous starts.

"The difference today was they bunched their hits in the first inning and got their runs," Padres manager Bud Black said.

After those first two shaky innings, the game was filled with some spectacular defensive plays, including two by Forsythe in the fourth, one by Roberts at third for the Diamondbacks in the fifth and an against-the-wall grab in center by San Diego's Cameron Maybin in the seventh. Arizona right fielder Justin Upton also made a nice sliding catch in the eighth.

Game notes
Bloomquist led off the game with a double to break an 0-for-12 streak. ... Andy Parrino, called up by the Padres before the game, flew out to center as a pinch hitter in his first career at-bat in the seventh inning. ... San Diego right-hander Aaron Harang (12-3), Saturday's starter, is 6-0 in nine road starts this season despite a 4.65 ERA away from Petco Park. ... Arizona left-hander Joe Saunders (8-11), who will pitch against Harang, has lost his last three decisions and has a 7.00 ERA over his last three starts. ... Arizona has won nine of 12 at home against San Diego.