OAKLAND, Calif. -- It is probably not wise for a last-place team in September to be overly boastful.

However, when an also-ran sweeps four games from the runaway division leader, one of the top teams in the majors all season, it can be excused for getting a little carried away.

"I think we're going to win a lot sooner than people think," Athletics right-hander Kendall Graveman said after he outdueled Houston Astros star left-hander Dallas Keuchel in Oakland's 10-2 win Sunday to complete a three-day whitewashing that included a doubleheader.

The A's took advantage of Keuchel's wildness during a three-run, tiebreaking sixth inning, allowing the bottom team in the American League West to record its second four-game home sweep of the season.

"What is comes down to," Graveman said, "is that these are guys who care about each other. Guys who won't quit. That defines these young guys. Guys who don't know any better."

The young bombers got rolling after Keuchel left a 4-1 game, with Ryon Healy belting a two-run homer in the seventh inning, and Boog Powell and Matt Olson hitting two-run shots in the eighth.

Another of the new, young core -- third baseman Matt Chapman -- had the first of Oakland's four homers. That combined with Graveman's six-inning, one-run pitching to help the A's turn the tables on Houston, which had entered the series having won 10 straight in Oakland.

"I think you probably let your guard down a little bit just being a human being and seeing the large gap," Keuchel said of a possible Astros letdown in the series. "But it's not like we're coming to the park not trying to win."

The loss kept the Astros' magic number for clinching the AL West at seven over the Los Angeles Angels, who won Sunday at Seattle.

With a 13-game lead in hand, the Astros visit the Angels for a three-game series beginning Tuesday.

"That's September baseball. It's funky," Keuchel said. "We'll right the ship. I firmly believe we'll be back on our game come L.A. and finish this road trip strong."

A sixth-inning RBI single by the Astros' Alex Bregman offset a Chapman solo homer in the fifth inning, his 12th of the season, sending the Keuchel-Graveman pitchers' duel tied 1-1 into the bottom of the sixth.

After Jed Lowrie led off with a single, Keuchel provided all the offense for the A's, walking Khris Davis, Olson, and one out later, Chapman to force in the go-ahead run.

Keuchel then hit Mark Canha in the left toe with a pitch, delivering another run, before issuing a fourth walk in the inning to Marcus Semien to force in a third run and give Oakland a 4-1 lead.

Keuchel (12-4) was pulled after the Semien walk, having allowed four runs on six hits in 5 2/3 innings. He walked four and struck out four in his first loss this season against the A's after three earlier wins.

"He threw a lot of close pitches (that) didn't go his way," Astros manager A.J. Hinch said. "Got a little unlucky. He wasn't all over the place even though his walk total's going to be high. He was one ground ball away."

Healy's homer, his 24th of the season, came off Astros reliever Francis Martes one inning later to increase the Oakland advantage to 6-1.

Graveman (5-4) was pulled at that point, He allowed five hits, walked two and struck out three in his 104-pitch effort.

"With Keuchel, you know it's going to be a low-scoring game," Graveman said. "As a starting pitcher, you know if you hang in there long enough, these guys are going to score enough runs for you."

Pinch hitter J.D. Davis hit a solo homer, his fourth of the season, off the third A's pitcher, left-hander Sam Moll, leading off the eighth inning to pull the Astros within 6-2.

Oakland closer Blake Treinen struck out pinch hitter Carlos Beltran with two on and two out in the eighth to preserve the four-run lead, setting the stage for the homers by Powell, his third, and Olson, his 17th, in the bottom of the inning.

"It's a great attribute to have to have a killer instinct," A's manager Bob Melvin said of his team's late offensive flurry. "They do feed off each other. There's a lot of encouragement, a lot of unity in the dugout we haven't had here in a while."

Healy and Canha had three hits apiece for the A's, who have won five in a row, matching a season best.

Jose Altuve and Carlos Correa each collected a double and a single for the Astros, who despite the four losses won the season series from the A's 12-7.

Astros pitchers walked eight batters in the game and 25 in the series.

NOTES: The last time the A's recorded two four-game sweeps in the same season was 1977. ... Astros CF Jake Marisnick was ejected in the fifth inning for arguing a called third strike. ... Athletics hitting coach Darren Bush planned to use the day off Monday to check on damage to his home in Englewood, Fla., which is just north of Fort Myers on the state's west side. The area was expected to take a big hit in Hurricane Irma's path. Bush has informed A's manager Bob Melvin if damage was severe, he would need a couple of days away from the team. ... After Monday's off-day, the A's begin a series Tuesday in Boston against the Red Sox. ... Astros manager A.J. Hinch announced Sunday that RHP Collin McHugh (avulsion in right middle fingernail) would miss his scheduled start Thursday against the Angels and be replaced by RHP Brad Peacock. The injury is not considered serious, and the plan is for McHugh to return during the series against the Chicago White Sox on Sept. 19-21. ... Astros C Juan Centeno (mild concussion) sat out Sunday and likely will need more time off after getting hit in the helmet on a 2B Jed Lowrie backswing Saturday.