Colin Clark added a goal and an assist for Houston, which moved into a tie with Kansas City at 27 points.
Seattle (38 points) stayed third in the Western Conference.
Clark scored in the 7th minute to put Houston ahead. Will Bruin crossed it from the left side, and Ching couldn't get it under control in the middle of the box before Seattle's Tyson Wahl tried a clear that went to Clark, who beat Seattle goalkeeper Kasey Keller from just outside the six-yard b
Ching made it 2-0 in the 23rd minute on a header from about six yards off a cross from Geoff Cameron on the left.
Alvaro Fernandez cut the lead to 2-1 with a penalty in the 37th minute after Fredy Montero was taken down in the box by Corey Ashe.
Ching extended the lead in the 70th after getting a cross from Clark from the right box in front of an empty net for the tap-in.