The sweep is only the third of the year for the Astros, all of which have come on the road.
"You come into a series and you want to win the series, and you put yourself in a position to win the first two games and having an opportunity to sweep," Astros manager Bo Porter said. "I felt like the guys responded well. They swung the bats well, Peacock set the tone on the mound, and we played well enough to come out of here with three wins."
The Astros ended a string of 20 consecutive games in 20 days, going 9-11 in that stretch, and improved to 6-5 in September by winning their 50th game of the season. Porter said a strong finish could only help his young club heading into the fall.
"It's very important," he said. "It's something we talked about heading down the stretch at the end of the year to let's build some momentum moving toward next year. As we go series by series, our goal is to win every series the rest of the season."
Peacock (5-5) began the season in the Astros' rotation and struggled through five starts before being moved to the bullpen and eventually getting sent down to Triple-A. He came back to Houston for three outings in relief in the middle of the season before rejoining the rotation Aug. 4. Peacock is 4-2 with a 3.38 ERA in seven starts since.
"Tonight, I was able to throw [the fastball] for strikes again and kept the guys off balance and let the defense do the work," Peacock said. "They did a great job for me tonight."
It's no secret Peacock's improved slider has helped him greatly in the last six weeks. He clearly trusts his off-speed stuff now, so much so he is comfortable throwing it when he gets behind in the count.
"That's been the biggest difference," Porter said. "When you're throwing 95, 96 [mph] and you're throwing your off-speed stuff, even when you're behind in the count, you'll get guys who can't wait for your fastball, and that makes his fastball that much better."
Behind Jarred Cosart, Jordan Lyles and Peacock, Astros starters allowed only two earned runs in 17 innings (1.06) in the three games against the Mariners.
"Our starting pitching has been outstanding," Porter said. "When you pitch well and you swing the bats and give those guys a little bit of a cushion, it allows them to attack the zone that much more, and I feel like they've done a tremendous job with that all series."
For the second game in a row, the Astros roughed up a Seattle starting pitcher. This time it was Brandon Maurer (4-8), who was rocked for five runs and seven hits in three innings.
"I tried to do the same thing tonight as I did in the bullpen, and it worked all right the first inning, but then I couldn't find the zone the next few," he said.
Marc Krauss had an RBI double in the second to get the Astros going, and Carlos Corporan drove him home with an RBI single to make it 2-0. Houston added three more in the third to take a 5-0 lead, capped by a two-run single by Chris Carter.
The Astros are hitting .353 with runners in scoring position in September.
"You look at the quality of the at-bats in those situations, and guys are not chasing; they're getting pitches they can do something with and not fouling them off, and they're putting good swings on them," Porter said.
Peacock allowed two singles in the first inning, one of which was an infield hit, and gave up only one hit the rest of the way. That came on a solo homer by Kendrys Morales to start the fourth inning that was 100th of his career. Peacock sent down the final nine batters he faced following the homer.
The Mariners loaded the bases after two outs in the eighth inning, but Josh Zeid got Raul Ibanez to pop out to end the threat. Zeid then worked the ninth for his first career save.
"Obviously, they have a little bit of faith in me," Zeid said. "I was trying to be aggressive. Corporan said, 'We're going to stay away from [Ibanez].' Obviously you want to be on outer-third and not miss over the plate. I wanted to strike him out, but I knew with two outs he could put the ball in play. Soft contact would work there."