The Astros led 9-1 before the Mariners got one back in the fifth and added five more in the sixth, all off starter Charlie Morton (13-3).
"You can't hate how you win if you win," Astros manager A.J. Hinch said. "It was good for us, especially the last three innings with the guys we threw. That's exactly how you draw it up. All three were dominant. The way those guys responded and held it down was pretty nice."
Osuna pitched the ninth to earn his 10th save. The closer was acquired from Toronto last month and joined the team a week later after finishing a 75-game suspension for violating Major League Baseball's domestic violence policy.
Maldonado had three RBI and White had two. Maldonado was acquired from the Angels on July 26.
"Overall, the way we swung the bats was pretty impressive," Hinch said. "Today it was a complete offense. And Martin has come over and provided a nice spark for us."
Marco Gonzales (12-9) was pitching on eight days of rest but allowed eight runs and 11 hits before leaving with no one out in the fourth. Gonzales has given up 23 earned runs and 38 hits in his last 20 innings over four starts.
"I don't think Marco threw the ball that badly," Mariners manager Scott Servais said. "Obviously, it had been eight days since he'd been out there. They put some balls in play, got some hits, hit a few balls hard. It just wasn't a clean outing for him."
The Astros took a 2-0 lead in the first with an RBI triple for White before Gonzales' wild pitch enabled White to score from third. White's home run came in the ninth.
"It was a fun game today," White said. "I'm just trying to help this team any way possible. I've learned not to press and just enjoy playing with these guys."
The big inning for the Astros was the fourth, when they sent 10 to the plate and scored five runs to take an 8-1 lead.
Gonzales gave up six consecutive hits to start the inning before he was replaced by reliever Nick Rumbelow.
"I had trouble keeping them off-balance today," Gonzales said. "I think we have a lot of time left to get everything firing on all cylinders. This team has done a great job of when one part struggles, the other part steps up. We have September to get hot."
Maldonado's homer came one inning later to make it 9-1.
Oakland's 4-2 loss to Texas on Wednesday gives the Astros a one-game lead in the AL West.
Nelson Cruz and Mitch Haniger each had home runs for the Mariners. Cruz hit an upper-deck shot in the fourth for his 31st homer. Haniger's two-run homer in the sixth inning was his 20th of the season.
CANO AT THIRD
Robinson Cano started at third base, the first time in his 14-year career he has played there. Cano also hit his 525th double, tying him with Ted Williams for 45th of the career list.
MARINERS ROSTER MOVE
LHP Ross Detwiler was designated for assignment and Rumbelow was recalled from Triple-A Tacoma.
Astros: OF George Springer (quad soreness) did not play in the three games at Seattle. "We're all frustrated," Astros manager A.J. Hinch said about Springer. "We'll aim for Friday."
Mariners: LHP James Paxton (bruised left forearm) will not come off the DL this weekend in Arizona and probably won't make his next start until sometime next week.
Astros: LHP Dallas Keuchel (9-10, 3:59) is expected to start Friday to begin a three-game series in Anaheim.
Mariners: A three-game series at Arizona starts Friday, and RHP Erasmo Ramirez (0-2, 5.49) is the likely starter for the opener. Servais said the rest of the weekend will depend on when RHP Mike Leake is ready to return. Leake missed his schedule start Tuesday because of an illness.
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