But then a penalty kick by Houston's Brian Ching in the 83d minute clinched the victory for the Dynamo (6-5-5). Ching had been fouled by the Union's Gabriel Farfan.
Saturday's match was the Union's first chance this season to get a small measure of revenge against a Dynamo squad that knocked the Union out of the playoffs last year.
A pre-match rainstorm did nothing to cool conditions here, merely turning the brand new BBVA Compass Stadium from an oven to a sauna.
There may be something to speculation that the Texas heat and humidity gives the Dynamo quite a home-field advantage. They are undefeated in six home matches this season, but rather mediocre away from Houston.
The Dymano got on the board first in the 20th minute on a goal by Brad Davis, with assists from Macoumba Kandji and Boniek Garcia.
Garcia was making his MLS debut for the Dynamo, after the 27-year-old Honduran international star just started practicing with the team Thursday.
Of course, the Union made their own flashy new acquisition this week. Saturday was the first match new signee Bakary Soumare could have played with the Union, after he signed amid much fanfare Tuesday. But the 6-foot-4 center back and former MLS Defender of the Year finalist, did not play as he continues to work his way back from knee surgery three months ago.
The only offensive chance the Union really had in the first half was a shot that went just a foot wide-left in the 11th minute by Jorge Perlaza.
Saturday's match was the first of nine for the Union that will be played in the next 36 days. It gets no easier. The Union go from playing MLS runner-up Houston to playing at the league champ Los Angeles Galaxy Wednesday.