Houston led 4-1 before pinch-hitter Alberto Callaspo had a two-run single off Qualls (1-2). After Houston couldn't turn a potential game-ending double play on John Jaso's grounder, Jed Lowrie walked and Yoenis Cespedes tied it with a single.
"You've been throwing the ball well for quite some time so your expectations are really high," Qualls said. "When an inning like that happens, you let your team down and you don't feel good."
Qualls has now allowed runs in two straight outings for the first time since the opening week of the season after previously making 31 of 33 appearances without allowing an earned run. Qualls' blown save was his third in 14 save opportunities and first since June 12.
"I don't want to say they got lucky because, obviously, that's not the case," Qualls said. "But they just found some holes when they needed to and hit the ball on the screws when they needed to. I just didn't get it done."
Marwin Gonzalez homered off the left field foul pole in the first to give the Astros a lead. Enrique Hernandez had an RBI triple as part of a two-run fifth and an RBI double in seventh to give the Astros the 4-1 lead.
"Any time you lose games in the eighth or ninth inning, those are tough games to lose," Houston manager Bo Porter said. "We were in position to win the ballgame and just were not able to close it out."
Astros starter Scott Feldman allowed one run and five hits in seven innings. He rebounded after one of his worst outings of the season Thursday at Oakland in which he gave up six runs in 5 1-3 innings.
"It was better than the last one, obviously," Feldman said. "That lineup over there has given me a tough time my whole career, even when they weren't as good."
A's starter Jeff Samardzija gave up four runs and six hits with seven strikeouts in 6 2-3 innings.
Astros: Outfielder George Springer, who has been on the disabled list since July 20 with a right quad strain, took batting practice Tuesday. "It's big to be out here and just to get some swings," Springer said.
Right-hander Jason Hammel will try to get his first win with the A's after going 0-3 with a 7.11 ERA in his first three starts since being acquired July 5 from the Cubs. Houston lefty Dallas Keuchel, who is 9-7 with a 3.11 ERA, will try to follow up a solid outing in a 2-0 loss to Miami in the final game of the three-game series Wednesday.
ONE STREAK CONTINUED, ONE SNAPPED
Houston second baseman Jose Altuve extended his hitting streak to 11 games with his RBI single in the fifth. The hitting streak is Altuve's second-longest of the season after a 12-game hitting streak from May 8-21. Astros outfielder Robbie Grossman was 0 for his last 13 before a single in the fifth.
OAKLAND NEVER OUT OF IT
The win Tuesday was the A's sixth this season when trailing after eight innings and was the second time the A's scored at least six runs in the ninth this year. Oakland scored seven runs in the top of the ninth on April 25, also at Houston.