SAN DIEGO -- Pitching and defense were supposed to carry the offensively challenged San Diego Padres this year.

Two months into the season, though, the Padres look nothing like the spot-on team of 2010, which set a franchise record and were second in the majors with a .988 fielding percentage.

Chris Johnson homered and the Houston Astros used a five-run third inning to beat the sloppy Padres 7-4 on Thursday in a matchup of the NL's two worst teams.

The Astros (23-34), last in the NL Central, have won the first four games of a seven-game trip, their longest winning streak of the season. The Padres (24-33), last in the NL West, dropped to 9-21 at home, worst in the NL. They came in hitting a major league-worst .199 at home.

The Padres had three errors that helped the Astros score five runs in the third inning. San Diego has 46 errors, second in the majors to Houston's 47.

"I'm surprised," manager Bud Black said. "I thought our defense would be much crisper."

The Astros didn't have any trouble with spacious Petco Park. Johnson homered to left on a 1-0 pitch from Tim Stauffer (1-4) with one out in the fifth for a 7-2 lead. It was Johnson's sixth. That helped make a winner of Bud Norris (3-4).

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Norris went six-plus innings, allowing four runs and six hits while striking out six and walking two. Mark Melancon pitched the ninth for his fifth save in seven chances.

The Astros had 11 hits. Hunter Pence extended his hitting streak to 14 games with a third-inning single.

Houston jumped on San Diego for five runs on just three hits in the third, when the Padres committed the three errors, including a catcher's interference. The first four Astros reached and scored, and Houston sent 10 men to the plate.

Carlos Lee had an RBI double and Brett Wallace an RBI groundout. J.R. Towles was credited with an RBI when shortstop Jason Bartlett bobbled his slow grounder, allowing Towles to reach and Lee to score. Norris drove in a run with a fielder's choice and another run scored on the play on second baseman Logan Forsythe.

"From the get-go, I didn't execute from the first couple of hitters who got on and put the ball in play," Stauffer said. "One of those innings you want to forget about, one of those bad innings."

Johnson also had an RBI single in the second.

Stauffer allowed seven runs, five earned, on eight hits in five innings, struck out four and walked two.

The Padres got consecutive RBI singles by Chase Headley, who extended his hitting streak to 12 games, and Ryan Ludwick in the third, and consecutive sacrifice flies by pinch-hitter Chris Denorfia and Eric Patterson in the seventh.

Notes

The Padres said nearly 1,000 season-ticket holders donated their tickets to military members and their families. Of those, 32 were in the Sony Home Plate Club, which at $325 are the most expensive seats at Petco Park. ... Black said C Nick Hundley, on the disabled list because of a strained muscle in his right side, will do drills on Friday and if everything goes well, will begin a rehab assignment at Triple-A Tucson. ... It was the seventh straight road game in which the Astros have 10 or more hits.