OAKLAND -- The A's erased a sizable deficit to halt the first-place Astros' seven-game winning streak, getting a game-tying grand slam from Marcus Semien in the seventh inning and a game-winning single from Jed Lowrie in the ninth to pull out a wild, 9-8 series-opening victory at the Coliseum on Friday evening.
The ninth-inning rally against Astros closer Ken Giles began with a leadoff homer from Boog Powell, tying the game after Houston had temporarily regained the lead in the top half of the frame on Josh Reddick's two-out RBI double. Semien kept things going with a base hit, Matt Joyce drew a walk, and Lowrie sent an 0-1 fastball to left-center field for the A's 10th walkoff win of the season.
"That's a good team, and you gotta just continue to grind," Lowrie said. "They've got a young core over there that's been there for a while, so they've got a lot of chemistry, a lot of good players, and I think that's what they're trying to build here right now."
Reddick finished with three hits and four RBIs against his former team, reaching base five times. The outfielder was one of three players -- joining Jose Altuve and Yuli Gurriel -- to hit a two-run homer for the Astros, who were denied their 11th consecutive win at the Coliseum.
"That's a tough loss. We hadn't lost here in a long time and we'd played really well recently," Astros manager A.J. Hinch said. "Couple of chances that we lost in some big moments, and a very winnable game, but it didn't work out."
Astros starter Collin McHugh was forced out of action after just three innings because of a right middle fingernail tear. The right-hander scattered four hits before his sudden departure, including a two-run homer to rookie Matt Chapman in the second and a solo shot to Joyce in the third.
"It's the same issue I had a couple years back, where the fingernail just digs into the nail bed underneath it," McHugh said. "With the doubleheader tomorrow, you'd like to save the bullpen as much as possible. Didn't happen tonight. We'll work this week and try to get it back healthy for the next start."
A's starter Jharel Cotton was haunted by the home run yet again, surrendering all three Astros blasts. The rookie right-hander, who has yielded a combined 12 home runs in his last 34 innings, was responsible for seven runs and as many hits across five innings.
MOMENTS THAT MATTERED
A boost from Boog: The A's were trailing, 7-3, entering the seventh when they put each of their first two batters on base and turned to Powell to keep things in motion. The speedy No. 9 hitter did just that against righty Luke Gregerson, beating out an infield single by sliding head-first into first base to load the bases, setting the stage for Semien's third career grand slam. More >
"We had heard from the moment we got him back that he played the game really hard," A's manager Bob Melvin said, "so the slide into first doesn't surprise you."
Raul in relief: The A's were simply trying to stay afloat when right-hander Raul Alcantara entered a 7-3 game in relief of Cotton in the sixth inning for his first Major League appearance since April 23. Alcantara, who spent the majority of his season with Triple-A Nashville, responded with two scoreless innings, inducing an inning-ending double play from Gurriel in the seventh ahead of Oakland's comeback efforts.
"That was key," Melvin said. "At the time, it's 7-3 and we're trying to get some innings and try to get him comfortable again. But as it turns out, those are two big innings. Looked like he was throwing harder, and everyone's been saying in development, maybe a relief role is probably a better spot for him."
WHAT'S NEXT Astros: The Astros will start right-handers Charlie Morton and Brad Peacock for the team's second consecutive Saturday doubleheader, which begins at 3:05 p.m. CT. Morton, who is 11-6 with a 3.87 ERA on the season, allowed two runs in five innings against the Mets to get the win in the first game Sept. 2. Peacock followed that up by allowing one run in 5 1/3 innings in the second game but didn't get a decision. He owns a 10-2 record with a 3.05 ERA on the year.
A's: Right-hander Daniel Gossett, who is 0-2 with a 5.40 ERA in two career starts against the Astros this season, will be on the mound for the first game of Saturday's doubleheader at the Coliseum, beginning at 1:05 p.m. PT. Right-hander Daniel Mengden gets the nod for the second game. It will be Mengden's first big league start since June 3 and fourth in his career against his former Astros organization. He posted a 7.63 ERA in his first three outings.