SAN DIEGO -- A fifth-inning walk to Arizona's Stephen Drew meant the difference between a good outing and a bad one for Chad Gaudin. The Padres' hitters, meanwhile, haven't had a good showing at home this week.

And for the fourth straight game, those factors added up to a Padres' home loss.

Buoyed by a four-run, fifth-inning rally and the strong pitching of Doug Davis, the Diamondbacks shut out the Padres 8-0 in front of 22,426 at Petco Park on Friday night. Before this week, the Padres had lost only six of 23 games at home.

"Just a couple of things could have been different," said Gaudin, who allowed five runs on six hits and four walks. "In those situations, you've gotta make some key pitches, and I feel the walk to Drew, I could have got out of it right there. And I prolonged it by getting the guy on, and you can't do that. … One thing turns into another, and you get four runs scored."

The Diamondbacks held a 2-0 lead when Drew stepped to the plate in the fifth inning with Gerardo Parra on second base and two outs. Gaudin quickly got ahead of Drew 1-2 in the count. But Drew remained patient and took three straight balls to earn a walk. Mark Reynolds, who had three hits, followed with a single to make it 3-0 and Chris Snyder then sharply singled in two more runs to blow the game open.

"He had a chance by getting an out before those two singles … it still could have been a 2-0 game after five," manager Bud Black said. "Snyder's was the back-breaker."

Especially with Davis on the mound. As he has done often in his career, Davis (4-3) made it look easy against the Padres.

The left-hander found trouble only twice during an 109-pitch outing as he scattered three singles and four walks. Other than Chase Headley's single to right field in the sixth inning -- a play in which Justin Upton threw out David Eckstein trying to score -- the Padres didn't come close to making a dent against Davis.

Using a sweeping curveball, Davis kept the Padres off-balance, striking out five.

"He was commanding three pitches," said shortstop Josh Wilson, a former teammate of Davis in Arizona. "He's kind of deceptive and varies his windup times. … Some of those things upset the timing and rhythm."

The loss of outfielder Scott Hairston to a biceps injury has weakened an already-struggling Padres' offense. Entering Friday, the Padres were hitting .238 and averaging 3.94 runs per game. The team's .391 slugging percentage ranked 13th among the National League's 16 clubs.

With Hairston out, the Padres' production has dipped further through the first four games of the homestand, as opponents have even less reason to pitch to slugger Adrian Gonzalez. Including Friday's four-hit shutout, the Padres are 25-for-126 (.198) with nine runs and four extra-base hits in the last four games.

"We need our guys in front of Adrian to get on base and the guys behind Adrian to knock in runs," Black said. "… This is not a one-person problem."

A lack of hitting at home, however, is nothing new to the Padres, who batted .209 during their 9-0 homestand last month. What keyed that run, and has been absent over the last four games, was strong pitching.

Out of the gate, Gaudin (2-4) looked impressive. Following a nine-strikeout, no-walk performance at Colorado on Sunday, Gaudin threw first-pitch strikes to 10 of the first 13 batters he faced and allowed only one run on a solo homer to center field by Arizona's Chris Young.

But by the fourth inning, Gaudin was falling behind in the count early, and it caught up with him during his fifth and final inning. Felipe Lopez started the inning with a one-out single, and Parra doubled into the left-field corner to drive in Lopez. Gaudin fought back and struck out Upton before walking Drew. That set up Reynolds' broken-bat single and Snyder's liner to center.

"They string together a couple of good hits, hit some good pitches and have big innings," said Gaudin, who threw first-pitch strikes to only three of the last 12 batters he faced. "I think I'm crushing myself to make great pitches all the time, and last time I just didn't worry about it. … I have to get myself back to attack mode."