Castro's double off Charlie Furbush (2-5) and Brandon Barnes' pinch-hit RBI single later in the eighth aided a gem from Oberholtzer (4-1) in his sixth major league start. The young lefty did not permit an extra-base hit and walked just one in a 113-pitch effort that halted a string of five straight Houston losses.
Hisashi Iwakuma matched zeros with Oberholtzer for the game's first seven innings before being removed for Furbush in the eighth. The Seattle righty scattered six hits and struck out seven while issuing just one walk.
Iwakuma was lifted after 99 pitches despite setting down 10 of the final 12 hitters he faced. Furbush, on the other hand, was greeted by Jose Altuve's third hit of the day -- an opposite-field double to open the bottom of the eighth. Castro followed with a deep drive into the gap in right center that easily brought home the game's first run.
After taking third on Matt Dominguez's flyout, Castro came around when Barnes dropped down a well-placed bunt as part of a successful suicide squeeze that pushed the lead to 2-0.
Oberholtzer, who retired the side in order in both the seventh and eighth, did give up a one-out single to Kyle Seager that brought the tying run to the plate in the ninth. The rookie was up to the task, however, getting Kendrys Morales to foul out before inducing a game-ending fly ball from Franklin Gutierrez.
Seattle's best scoring chance came in the third, when Justin Smoak drew a leadoff walk and later raced to third on Brad Miller's two-out single. Oberholtzer was able to strike out Nick Franklin swinging, though, and end the threat.
Outfielder Trevor Crowe, recalled by the Astros from Triple-A Oklahoma City prior to the game, went 2-for-4 with a double while starting in center field ... The Mariners recalled ousted closer Tom Wilhelmsen from Triple-A Tacoma on Sunday, with the right-hander recording the final out of the bottom of the eighth ... Seattle had prevailed in six straight meetings with Houston and lost for only the third time in 10 visits to Minute Maid Park this season.
09/01 19:37:25 ET