Oakland maintained its three-game lead over the Rangers in the American League West.
"We played some kind of ugly for six innings but stayed with it," manager Bob Melvin said. "For me, that was the overriding feeling at the end of the game, that as badly as we played, we stuck with it and didn't give up and put our heads down and say, 'Oh, we're just having a bad game.'"
It was Reddick's two-run shot that made the difference, with the right fielder going deep on a full count against lefty Wesley Wright to right field in the eighth to give the A's their first lead.
Young's homer was lined to left off former A's left-hander Travis Blackley in the seventh -- his ninth of the year and eighth in 22 career games at Minute Maid Park -- to spark Oakland's offense, which, to that point, had put together an awful showing and finished 0-for-9 with runners in scoring position and left eight runners on base.
"That was the big at-bat that gave us the energy in the dugout we really needed to get going, especially since we had left so many runners on base early on," Reddick said of Young's at-bat. "That's just something we've been doing for a year and a half. Last year, it didn't matter if we were down by one or five, we felt like we had a chance to come back."
The A's made three errors in the first three innings and, it easily could have been four, had Josh Donaldson's mishandling of a ball hit off the bat of Justin Maxwell to lead off the second not been ruled a double.
Donaldson contributed with a leadoff hit in the sixth, a single off Astros starter Dallas Keuchel that was followed by a double from Nate Freiman and, ultimately, a sacrifice fly from Grant Green, who notched his first career RBI after making his third career error in the third.
With two on and two out in the third and the Astros leading 2-0, A's starter Tommy Milone induced a potential inning-ending popup from Maxwell. But second baseman Green, who initially called for the ball, slowed down while presumably hearing footsteps and watched the ball drop for a run-scoring error.
That was after a second inning in which shortstop Jed Lowrie's throwing error led to Houston's first run.
"This is definitely a ballgame we feel like we should have won," Astros manager Bo Porter said. "We put ourselves in position to win early, getting the lead, and I felt late in the game we did not execute the right pitches we needed to make to close it out."
Porter liked his matchup in Wright vs. Reddick. Turns out Reddick did, too.
"I was trying to sit slider," he said. "The last time I faced him, he threw me a lot [of sliders], so I was waiting for one of those. He tried to nibble away with his fastball, over and over, and after a 3-1 check swing, I got a little frustrated with myself and had to talk myself down a little bit. He threw one right down the middle, and fortunately I didn't miss it."
Milone lasted six innings and was charged with three runs (two earned) on five hits and one walk with five strikeouts before Ryan Cook entered for the seventh and left with a win in hand, following Sean Doolittle's scoreless eighth and a clean ninth from Grant Balfour, who earned his 26th save of the year and 44th in a row dating back to last year.
All three relievers struck out two batters and didn't allow a hit.
"The first couple innings, obviously something was off," Milone said. "I think, as a team, we just didn't feel comfortable. We were able to stay in the game and get those big hits when we needed them."