Darwin Barney and Alfonso Soriano each hit two-run home runs against Galarraga, who left the game after just five innings. In four starts with Houston, Galarraga has yet to pitch more than 5 1/3 innings.
"I thought my mechanics were way better," Galarraga said after Monday's outing.
The right-hander gave up 13 combined walks over his previous two starts.
"I think I got better," he said. "Maybe that doesn't sound right, because I [allowed] so many runs and I can't be happy with this start, but I feel my mechanics were way better [than] my last two starts."
The D-backs will send Ian Kennedy to the mound against Galarraga in Sunday's series finale at Minute Maid Park. Kennedy has struggled with the long ball all season.
Kennedy gave up two home runs on Tuesday against the Cardinals -- his 22nd and 23rd of the season. After Kennedy's breakout year in 2011, D-back's manager Kirk Gibson is still trying to put his finger on what has been the biggest difference in '12.
"He's not throwing the ball exactly like he was last year and he's having a little different luck," Gibson said on Tuesday. "Maybe not quite as much life on his ball, but he's learning how to deal with that."
As for the home runs, Kennedy said he is working to improve. He has given up nine home runs over his last five starts.
"You're going to give up home runs," Kennedy said after Tuesday's start. "It's part of the game. Any time I give up runs I'm going to try and make adjustments."
D-backs: Young in Houston
Even though he plays for the visiting club, Chris Young feels right at home when the D-backs play the Astros at Minute Maid Park.
"It's like a family reunion," said Young, who was born in Houston. "I have literally my entire family here. They come out to the games and show support. I get a chance to hang out with them afterward. It's always a lot of fun for me."
Young said he needed about 60 tickets for each of the D-backs' three games this weekend. And he certainly didn't disappoint his fans on Saturday with a four-hit, three-RBI performance.
"With the family here, you know that everybody's watching," Young said. "I've had some bad games, too, but even when I do, they still show support. It's really not too much added pressure."
Astros: September callups
The Astros' Triple-A affiliate in Oklahoma City is competing for a Pacific Coast League playoff spot, which could impact which players the Astros call up in early September.
"You don't want to take everybody from their club," Astros manager Brad Mills said. "These guys have been down there all year long and they put themselves in position to win something, and you don't want to devastate the whole club."
Mills said he has already had a handful of conversations with general manager Jeff Luhnow concerning who will join the club next month. As of right now, the team expects to call up catcher Carlos Corporan, as well as a pitcher or two and a handful of position players.