The Sounders established a new MLS record of 13 straight unbeaten results to begin a season. The LA Galaxy (1996, 2010), Kansas City Wizards (2000) and Real Salt Lake (2014) all opened with streaks of 12 undefeated matches.
Raul Ruidiaz added his 10th goal of the season in second-half stoppage time to tie for the league lead, and Seattle goalkeeper Stefan Cleveland made three saves to record his third shutout of the year.
The Dynamo dropped to 0-2-4 over their past six matches. Houston goalkeeper Marko Maric made four saves.
The Dynamo had a chance to tie in the 89th minute, but Maximiliano Urruti's right-footed blast went right into the midsection of Cleveland in the center of the net.
Houston had a corner kick in the second minute of second-half stoppage time, but Seattle's Fredy Montero cleared the ball away from the net.
Ruidiaz then put the game away in the fourth added minute when he broke in on goal. He received the pass from Brad Smith and tapped a right-footer past Maric for the clinching tally.
Seattle held a 19-11 edge in shots. The Sounders put six on target while Houston had four.
Seattle outshot Houston 10-6 in the first half and had three prime opportunities.
Ruidiaz sent a left-footer off the right goalpost in the seventh minute and also had a close-range right-footer go just wide to the left in the 24th minute. Montero was set up for a header in the 21st minute, but Maric made the save.
Houston's Memo Rodriguez had two good opportunities, but his right-footed attempt in the 17th minute and left-footer in the 29th were both saved by Cleveland.