The Seattle Sounders punished a late mistake through former Liverpool defender Djimi Traore and will leave Kansas City with three points.
Seattle goalkeeper Marcus Hahnemann's ejection, which he picked up from the bench, was the biggest talking point of the first half, though it had no real impact on what was a very tame opening period.
Chances were few and far between in the second half as well, with the play in and around the area broking down.
Kei Kamara came on in the second half for Sporting to a generous round of applause as he returned to MLS action for the first time since his loan spell to Norwich City, but his return couldn't spark a win. In fact, a late Seattle goal ruined his homecoming.
A mistake at the back from Aurélien Collin provided the opportunity, and Djimi Traore was on hand to poach the win for the Sounders.