OAKLAND, Calif. -- The Danny Valencia Show continued Sunday for the Oakland A's at the O.co Coliseum.

Valencia hit a solo home run in the fourth inning and a walk-off single with two outs and the bases loaded in the ninth, leading the Oakland Athletics to a 5-4 victory against the Houston Astros.

Since being claimed off waivers from Toronto on Aug. 3, Valencia has gone 7-for-16 (.438) with two doubles, two homers and four RBIs.

"We got a gift-wrapped present from Toronto, I promise you that," said A's right-hander Chris Bassitt, who allowed one run over 6 2/3 innings. "My goodness. How he got (designated for assignment) is shocking to every single person on this team, including coaches."

The walk-off hit was Valencia's fifth of his career.

After the A's scored twice in the bottom of the eighth to take a 3-1 lead, the Astros rallied to take a 4-3 lead in the top of the ninth on right fielder Colby Rasmus' three-run homer off A's closer Edward Mujica.

Oakland answered with two runs in the bottom of the inning against Astros closer Luke Gregerson, a former Athletic.

First baseman Mark Canha led off with an infield single, beating out a ground ball to shortstop Carlos Correa, then moved to third on catcher Josh Phegley's single to right. Gregerson struck out shortstop Marcus Semien. But after falling behind 3-0 to center fielder Billy Burns he issued an intentional walk, loading the bases.

With two outs, right fielder Josh Reddick hit a comebacker that bounced off Gregerson for an RBI single, driving in Canha to tie the game 4-4 and bringing Valencia to the plate.

"It wasn't hit very hard, but just enough to catch me off-guard, and it hit off the wrist," Gregerson said.

Valencia got ahead 2-1 in the count and drilled a single down the left field line, bringing Phegley home.

"Throughout that inning he was spiking his fastball a lot," Valencia said. "That really is his bread and butter, so I was going to look for an off-speed pitch. He threw me one first pitch that was good to hit, but I don't know if I was quite ready for it. Luckily he threw it again and he left it over the plate and I was able to get enough of it to shoot it in the outfield."

The A's beat the first-place Astros for the third straight time and took three of four games in the series. The A's moved to within 10 games of Houston in the American League West, their smallest deficit since July20.

"We're just going to battle," Phegley said. "It's not over, and we're still trying to win games."

Houston has lost six of the first seven games on their nine-game road trip.

"Every loss is bad, especially with all these close games," Astros manager A.J. Hinch said. "We've had a rough week."

Bassitt allowed just three hits, struck out a career-high 10 and threw a career-high 112 pitches. He threw his seventh straight gem since being recalled July 25 from Triple-A Nashville for the fourth time this season.

With the game tied 1-1, the A's rallied to score twice in the eighth inning. Phegley worked a leadoff walk against right-handed reliever Will Harris and moved to third when Semien lined an opposite field single to right. Burns brought Phegley home with a sharp single to left, giving Oakland a 2-1 lead.

Astros left-hander Tony Sipp came on and retired the first batter he faced, but Reddick sliced an RBI double to left.

Mujica got into trouble quickly in the ninth. Center fielder Carlos Gomez hit a leadoff single to left and moved to third on third baseman Jed Lowrie's single, bringing Rasmus to the plate. He launched Mujica's 91 mph fastball high and deep into the right field seats.

"It didn't turn out to be a big hit," Rasmus said of his 14th home run. "That's part of the game. They played us tough. I feel we'll turn things around."

Astros right-hander Mike Fiers made his first start for the Astros since coming to Houston from Milwaukee on July 30 in a trade and held the A's to one run on five hits over 6 2/3 innings in a no-decision.

Valencia put Oakland ahead 1-0 with his homer in the fourth. The Rangers pulled even with a run in the sixth. Second baseman Jose Altuve lined a one-out single to center. Then with two outs, shortstop Carlos Correa hit an RBI double to left-center.

NOTES: Astros LHP Oliver Perez, who was acquired from Arizona on Friday night in a trade, was activated Sunday and retired the only batter he faced in the seventh inning. ... Houston 1B Chris Carter made his second straight start, this one at DH, and went 0-for-3 as his average dipped to .180. ... Oakland LF Coco Crisp, who left Saturday's game following the second inning after having a nauseous reaction to medication, was in the lineup again Sunday. ... A's LHP Sean Doolittle (strained left shoulder) threw a bullpen session in Oakland on Sunday and will make his second rehab appearance on Tuesday, this time for Triple-A Nashville. He pitched a scoreless inning Friday for Class A Stockton.