OAKLAND, Calif. -- The Houston Astros had won seven straight games overall and 10 straight at the Oakland Coliseum going into the opener of their four-game series against the Oakland Athletics on Friday night.

Both streaks looked safe when Josh Reddick brought George Springer home from first with a two-out double in the top of the ninth, putting Houston ahead 8-7.

The A's had other ideas.

Rookie Boog Powell led off with a game-tying solo home run in the bottom of the ninth inning against closer Ken Giles, and Jed Lowrie had a walk-off RBI single later in the inning, lifting the A's to an improbable 9-8 victory.

"It's a frustrating loss for us, that's really one way to describe it," said Reddick, a former Athletic. "Those guys just hung around, had big hits in the right spot and that's what you got to do to win the game. We had some big hits as well. But they just got it in the last at-bat and ended up being on top. We've got to put it behind us and come back out here tomorrow."

Marcus Semien hit his third career grand slam, Matt Chapman hit a two-run shot and Matt Joyce had a solo homer for the A's.

Powell sent Ken Giles' 0-2 pitch into the right field seats for his second home run of the season.

"I knew he had the heater," Powell said. "He throws 98 to 100. I was just trying to go the other way with it and then he threw me a slider right where I like it, and it ended up going out."

Semien followed with a single, and Giles walked Joyce. Lowrie, a former Astro, singled to left-center, bringing Semien home to beat the Astros at the Coliseum for the first time since July 19, 2016.

"That's a good team," Lowrie said of the Astros. "You got to just continue to grind. They've got a young core over there that's been together for a while, so they've got a lot of chemistry, a lot of good players. I think that's what they're trying to build here right now."

Giles (1-3) took the loss, and Blake Treinen (2-4) got the win despite giving up a run in the ninth.

Chapman went 3-for-4 with his 11th homer for the A's. Joyce had a double to go with his 23rd homer. Ryon Healy went 3-for-4 with a double and scored a run.

Jose Altuve, Yuli Gurriel and Reddick each homered for the Astros.

Reddick went 3-for-3 with a two-run homer and two doubles. He drove in four runs and scored twice.

Altuve went 2-for-5 with a double and a two-run blast, his 22nd of the season, and scored twice. Gurriel hit his 17th homer, a two-run shot.

The Astros led 7-3 entering the bottom of the seventh, but Semien tied it with his second grand slam this season. His first came on July 31 in an 8-5 victory against San Francisco at the Coliseum.

Bruce Maxwell led off with a walk and moved to second on Chapman's single off Mike Fiers. Facing former A's reliever Luke Gregerson, Powell loaded the bases with an infield single, bringing Semien to the plate. He lined Gregerson's 2-2 slider over the left field fence.

"He's got a sinker and a slider that both go down pretty hard," Semien said. "He kind of buckled me on the first slider, but I got a good look at it. I chased one. I didn't think I went, but it was pretty close. I was just saying, 'I got to see the ball up,' and he threw one up."

Astros right-hander Collin McHugh left the game after three innings because of damage to his right middle fingernail, which tore away from the skin.

McHugh allowed three runs on four hits, including home runs by Chapman and Joyce, and left with the Astros leading 5-3.

"It's the same issue I had a couple years back, where the fingernail just digs into the nail bed underneath," McHugh said. "Cutting and bleeding, we couldn't get it to really stop. We put some superglue on it, tried a couple different things down in the dugout. Couldn't really get the result we wanted. I hate it. I hate it for tonight. I was feeling pretty good coming into today."

A's right-hander Jharel Cotton gave up a season-high-matching seven runs on seven hits over five innings. He allowed three home runs for the second straight game and the fourth time this season.

The Astros took a 2-0 lead in the top of the first when Springer had a leadoff walk and Altuve launched Cotton's 0-2 fastball for a home run to deep left.

Oakland pulled even in the second.

Healy led off with an infield single, and Chapman crushed McHugh's 2-2 changeup for a home run to center with one out.

Houston answered with three runs in the third to take a 5-3 lead.

Reddick smoked an opposite field, RBI double down the left-field line with two outs, and Gurriel sent Cotton's first-pitch changeup over the left-field fence for a two-run shot.

Joyce cut Houston's lead to 5-3 with a leadoff homer to center in the bottom of the third.

Reddick extended Houston's lead to 7-3 with a two-run blast in the fifth.

"He's been exceptional," Astros manager A.J. Hinch said of Reddick. "He knows the strike zone and he does a lot of damage. Obviously he loves hitting here. He's been under the radar and an under-appreciated, huge part of our team."

NOTES: Astros C/DH Evan Gattis (right wrist soreness) is expected to rejoin the Astros on Saturday and start at DH on Sunday against Oakland, manager A.J. Hinch said. Gattis played another rehab game Friday for Class A Quad Cities and went 0-for-2 with two strikeouts as the designated hitter. "All signs are pointing in the right direction. He feels really good," Hinch said. ... Astros RHP Michael Feliz (right shoulder discomfort) was activated Friday from the 10-day disabled list and pitched a scoreless fourth inning, despite allowing two hits. Before going on the DL, Feliz was 4-2 with a 5.04 ERA in 42 relief appearances over 44 2/3 innings. ... Oakland OF Jake Smolinski threw to bases and from as far as 135 feet for the first time since his right shoulder surgery on March 16. Since being activated from the disabled list Sept. 1, he has pinch hit and pinch run. A's manager Bob Melvin said Smolinski might be medically cleared to play the outfield by mid-September.