Martins tallied in the 21st minute and Chivas defender Mario de Luna headed a cross into his own net in the 33rd as the Sounders (5-4-3) bounced back from a 4-0 loss last weekend to the Los Angeles Galaxy on the same field and the first U.S. Open Cup defeat in team history three days later.
Chivas USA (3-8-2) lost its fifth game in a row and saw its winless streak hit eight games, seven of them losses six by shutout. The Goats, who dismissed head coach Jose Luis "Chelis" Sanchez Sola on Wednesday, have been outscored, 15-1, in their last five games.
Youth academy director Sacha van der Most was in charge of Chivas, with new coach Jose Luis Real expected to arrive from mother club Deportivo Guadalajara early next week.
Seattle went ahead after three quick passes along the left flank sliced up Chivas' defense. The last, from Lamar Neagle, had Martins streaking alone into the box, and he chipped the ball over Chivas goalkeeper Dan Kennedy.
The Sounders doubled the advantage a dozen minutes later. Mauro Rosales took a pass on the right wing from DeAndre Yedlin and sent a looping cross toward the far post, nowhere near a teammate. Chivas right back Mario de Luna tried to nod it back to Kennedy but got too much of the ball, sending it past the goalkeeper and into the net for an own goal.
Martins, who was red-carded for a 71st-minue foul on Chivas midfielder Gabriel Farfan, nearly netted a third before halftime, but Kennedy made a fine reaction save on his header from 7 yards.
Midfield leader Osvaldo Alonso returned from a groin injury for the Sounders, but he departed after just 20 minutes with an unrelated thigh injury.