Hahn, who allowed 10 runs (nine earned) in two innings vs. the Astros at the Coliseum last Thursday, gave up six runs in two-plus innings in a rematch with the American League West leaders..
"Last one, I thought it was just a bad start, so I put it behind me," Hahn said. "It happened again, so now I need to look into it, and get back on the same page I was on early on.
"It's tough for me to analyze it right now, but it's unacceptable. Whatever it is, I have to find something. It might be something small to get me back on track, because I can't keep having outings like this, especially when our lineup's been so good and keeping us in ballgames. This is a game we need to win, and I put us in too big of a hole to do that."
Oakland hit a season-high five home runs, including two by Khris Davis, yet lost a 5-4 lead after the top of the third inning. Hahn, who yielded a pair of runs in each of the first two innings, boarded the first two batters of the third, prompting his departure.
Lefty Josh Smith allowed both runners to score, and then three more, as Houston took a 9-5 lead into the fourth.
"It's tough when you go out there and you're giving it everything you have, but your stuff just isn't coming out, or you're not getting the results that you want," Hahn said. "I think I had the right mindset coming into the start. I was prepared for it. I think I was very motivated to pitch well against these guys. Just didn't happen."
Hahn had a 3.56 ERA before last week's meeting with the Astros. After Wednesday, he owns a 5.30 mark.
"He was pretty one-sided where he was throwing the ball, and couldn't get the ball to the other side of the plate, and you can't just stay on one side of the plate with these guys," manager Bob Melvin said. "Early in the season, probably had a little more velocity. A lot of guys are down a little at this point right now, but his curveball wasn't as good, his command wasn't as good, so it's something he's going to have to tighten up a little bit."
Jane Lee has covered the A's for MLB.com since 2010.