Valbuena, who started the scoring with a blast in the first inning, opened the eighth with a homer to right on 1-1 pitch from Danny Farquhar (0-1). It was his fifth this season.
It was the first home run allowed by a Mariners reliever this season. Jed Lowrie added an RBI single in the inning.
Tony Sipp (1-0), who worked the seventh and eighth, picked up the victory.
Over the last seven games, those 3-4-5 hitters have have combined to hit .452 eight doubles, eight home runs and 21 RBI.
Mariners: SS Chris Taylor (fracture right wrist) appears fully recovered and is playing for the Triple-A Tacoma Rainiers.
Astros: RHP Josh Fields (strained right groin), who began the season on the DL, was expected to pitch two innings Monday for Triple-A Fresno. LHP Brett Oberholzer (left index finger blister) was expected to throw live BP Monday at extended spring in Kissimmee.
Mariners: RHP Taijuan Walker (0-2, 17.18) made progress, albeit slight, from his first start to his second. In his season opener, he allowed nine runs in 3 1/3 innings then cut it back to five runs in four innings. However, all three of his career victories have come against Houston, 3-0 with a 2.91 ERA.
Astros: RHP Colin McHugh (2-0, 1.54) likes Safeco Field, 2-0 with a 0.61 ERA (one run in 14 2/3 innings) with 16 strikeouts in his two career starts. In his last start at Safeco, Sept. 9, he allowed one hit in eight innings. He appears unaffected by a tender finger that limited in his opening start.
PLAYER OF THE MONTH?
Nelson Cruz had six home runs, 10 RBI and hit .500 for the week, good enough to be named AL Player of the Week, April 13-19. "Probably player of the month. I think it would be hard pressed to beat that," Manager Lloyd McClendon said. It was Cruz's fourth career POW honor and the third team in which he did it. Cruz, who started the season at 1-for-15, said what turned him was "just a feeling. One swing can change whatever you're feeling at the plate."
REST FOR CARTER
Astros 1B Chris Carter, mired in a 3-for-40 slump, did not start. He hit 37 home runs with 88 RBI last season but does not have an extra-base hit or a RBI this season, with 17 strikeouts. "It takes 30 to 40 at-bats to get to a bad number and it's going to take 30 to 40 to get back out of it," manager A.J. Hinch said. "It's going to take more than one day for him to feel great about it." Carter entered the game in the sixth as a pinch hitter and struck out, and again in the ninth.