Houston, who finished last season at the bottom of the Western Conference, gave no quarter to the defending champions.
Their aggressive play led to an early goal from Erick Torres and they held on for the home win.
Torres scored his first goal since playing for Chivas in 2014 as his free kick in the 20th minute from just outside the penalty box eluded the outstretched arms of a diving Stefan Frei.
Romell doubled the lead in the 42nd minute, curling a shot from 20 yards out into the top left corner of Frei’s net.
The Dynamo took the two-goal lead into halftime with their confidence high.
A vaunted Sounders lineup including returning veteran Clint Dempsey, Nicolas Lodeiro and rookie of the year Jordan Morris produced little in the first 45 minutes.
Dempsey finally got the Sounders on the board in the 58th with his first goal in more than five months. He missed Seattle’s run to the MLS Cup crown after his season ended prematurely because of an irregular heartbeat.
The game was one of seven on the second day of the new season.
FC Dallas extended their streak of season-opening victories to six with a 2-1 triumph over the Galaxy in Los Angeles.
Kellyn Acosta scored the game-winner with a shot from the top of the penalty area after getting past Galaxy defender Daniel Steres.
The 21-year-old’s sixth career goal not only extended Dallas’ run of success in season openers, it ended their winless run in regular-season games in Los Angeles, where they hadn’t won since September of 2009.
Maximiliano Urruti also scored for Dallas, who claimed last season’s Supporters Shield as the team with the best regular-season record.
Giovani dos Santos converted a penalty for the Galaxy, whose squad included seven MLS newcomers with new coach Curt Onalfo at the helm.