BY PAUL GACKLE

OAKLAND — Brandon Moss gave Jeff Samardzija more run support in one swing than he’s received in two-thirds of his starts this season.

Samardzija has received the fourth lowest run support in the majors this season, but the A’s supplied plenty of offense on Thursday, including a grand slam from Moss, as they defeated the Houston Astros 13-1 at the O.co Coliseum.

“When you have a lead, you can take a deep breath and pound the zone,” Samardzija said.

The All-Star right-hander received little offensive help when he was a member of the Chicago Cubs earlier this year. The Cubs provided four or more runs of support in only four of his 17 starts and he received as much offense from the A’s on Thursday as his former club provided in his last six outings with the team.

The American League’s top run-scoring team opened up the scoring with a three-run, two-out rally in the third inning. Josh Donaldson picked up his 72nd RBI of the season, scoring Josh Reddick with a single to right and then Eric Sogard scored on a wild pitch after swiping third in a double steal with Donaldson.

The All-Star third baseman eventually scored on a single to right by Derek Norris.

After adding a run in the fourth, the A’s gave Samardzija a 7-1 cushion in the sixth when Moss smacked his third grand slam of the season with Coco Crisp, Donaldson and Sogard aboard.

“Twelve RBI in three at bats — that’s not fair,” A’s Manager Bob Melvin said, referring to Moss’ three grand slams. “You’ve got guys who have to work to get 12 in a month and he’s got them in three at bats.”

Samardzija said the grand slam changed the mood in the dugout.

“That really broke it wide open,” he said. “It made the dugout nice and loose.”

The A’s tacked on a ninth run later in the inning and added four more in the eighth, allowing Samardzija (2-1) to cruise to an easy victory.

Josh Reddick continued to impress in his return from the disabled list. He went 2-for-4 with two doubles and an RBI returning to Wham’s “Careless Whisper” as his walk-up music one night after using “Wild Thing” to the chagrin of the home crowd.

Whatever music he uses, Reddick’s hitting the ball, going 4-for-8 in two games.

As the bats piled it on, Samardzija continued to impress his new club, surrendering one run on five hits in eight innings of work. He’s pitched at least seven innings in all four of his starts with the A’s.

“He goes out there and takes nothing for granted,” Melvin said. “He’s just as comfortable, probably, in two or three-run games as he is with some runs.”