Kikuchi (1-1) did not allow a hit until Carlos Correa doubled to deep right-center field with one out in the seventh.
Correa was stranded when Yuli Gurriel grounded out to Kikuchi and Aledmys Diaz grounded out to shortstop.
That was the only hit allowed by Kikuchi, who pitched seven innings, struck out seven and walked two, throwing 61 of 95 pitches for strikes. Kikuchi walked Alex Bregman in the first and Myles Straw in the third inning, then retired 11 in a row.
Kikuchi, a 30-year-old left-handed pitcher from Japan, entered Thursday with a career record of 8-16 with a 5.42 ERA since joining Seattle in 2019.
Anthony Misiewicz pitched a perfect eighth, and Kendall Graveman a one-hit ninth for his third save, completing a two-hitter.
Trammell hit his fourth home run of the season in the third inning, a ball that appeared to graze the glove of a leaping Chas McCormick at the right-field wall.
Seattle stopped a four-game losing streak. Houston lost for the second time in the last eight games.
Houston starter Luis Garcia (0-3) allowed three hits and struck out six in five innings. The Astros bullpen held Seattle scoreless in four innings and has allowed just one run in its last 14 innings.
Mariners: LHP Marco Gonzales was placed on the 10-day injured list with a left forearm strain and is expected to miss a couple starts, manager Scott Servais said. Gonzales had an MRI on Wednesday. RHP Domingo Tapia was added to the active roster from the taxi squad. … LF Mitch Haniger (undisclosed) missed a second straight game. Servais said he wanted to play but held him out as a precaution. CF Kyle Lewis (rest) was also out of the lineup.
Astros: DH Yordan Álvarez (health and safety protocols) could be available for Houston’s weekend series in Tampa, manager Dusty Baker said, adding that Álvarez is still taking more tests and is not 100% yet. He was placed on the injured list on Wednesday.
Mariners: RHP Chris Flexen (2-1, 2.74 ERA) will start for Seattle on Friday night when the Mariners host the Angels.
Astros: RHP Lance McCullers Jr. (1-1, 4.58 ERA) will pitch in his hometown for the first time since 2018 as Houston starts a three-game series at Tampa Bay on Friday.