Houston's Erik Bedard (3-7) no-hit the Mariners over six innings, but thanks to a pair of walks, two passed balls by Astros catcher Jason Castro and a Nick Franklin sacrifice fly, found himself in a 2-2 tie.
Bedard was pulled after issuing a one-out walk in the seventh to Justin Smoak and was replaced by Jose Cisnero, who fanned Jason Bay.
But Mike Zunino drew a base-on-balls and Saunders followed with the Mariners' first hit -- a ringing double to the center field hill that sent Smoak and Zunino home for the tie-breaking runs.
Hisashi Iwakuma (9-4) earned the victory, allowing two runs on seven hits over seven innings. He walked two and struck out seven.
Bedard was saddled with the loss despite not yielding a hit over 6 1/3 innings. The veteran left-hander walked five and struck out 10.
Jose Altuve and Castro each drove in a run for Houston, which dropped a fourth straight.