The Earthquakes had the better of the play in the first half, but had to wait until the 48th minute for Martinez to fire them in front.
San Jose has won two times in its last four games as the club continues to try and dig out from an early-season hole, while Seattle lost for the third time in four games and continues to struggle with consistency.
Seattle goalkeeper Michael Gspurning produced a pair of fine saves in the first half to deny a bicycle kick from Martinez as well as a close-range header from Alan Gordon.
However, the netminder was injured in the first half and was substituted at the break, with Andrew Weber taking his place.
But Weber was picking the ball out of his net just three minutes after taking the field as Steven Lenhart's driven ball into the penalty area found Martinez, who cut back past a defender and fired a shot beyond the reach of Weber.
Seattle failed to register a shot on goal in the first half, and the Sounders weren't much better in the second 45 minutes with a flicked header from Marc Burch that sailed over the crossbar in the last 10 minutes representing one of the better chances for the visitors.
The frustrating evening was capped off for Seattle when midfielder Osvaldo Alonso was sent off just before the final whistle after an altercation with San Jose's Dan Gargan.
07/14 00:47:31 ET