The former Inter Milan, Newcastle United and Levante striker slotted home in the 27th minute to help the Sounders to a 1-0 victory at Colorado Rapids despite not being tipped to start because of injury problems.
Seattle boss Sigi Schmid was thrilled with the effort Martins gave after Eddie Johnson was withdrawn because of a hamstring injury.
"He was a real trooper," Schmid said.
"At first, we didn't expect him to start this game, but then with the situation with Eddie Johnson when he went down on Friday, we said, 'Hey, you think you've got 45 minutes in you?' He said 'yeah,' so I said I was going to start him.
"He gave everything he had for as long as he could, and obviously scored a great goal."
Despite the win, the Sounders remained bottom of the Western Conference table with just five points from six outings.