Houston jumped over Montreal into third place in the Eastern Conference with 47 points, five behind front-running New York. Montreal has a game in hand on Houston, but the Impact has picked up just one point in their last four games.
It was the third win in the last four outings for the Dynamo.
The game's only goal was set up by a long, high pass from Boniek Garcia in midfield to Giles Barnes. He quickly got it to Clark, who scored from 25 yards out.