Saunders (1-1) scattered six hits over 6 1/3 scoreless innings, issuing only one walk while striking out five.
Carter Capps and Charlie Furbush combined for 1 2/3 frames of shutout relief and Tom Wilhelmsen notched his third save with a 1-2-3 ninth as the Mariners claimed the first of a three-game set.
Kendrys Morales supplied a pair of run-scoring hits for Seattle.
Phil Humber (0-1) was touched for three runs on five hits in a six-inning start, allowing one walk while striking out two for the Astros, who fell for the sixth time in seven games to start the season.
Celebrity Breakups and divorces of 2014 [PHOTOS]